Regex tooling: formula gene grouping, content patches, def validation

Three regex-powered content tools (phase G5):

- Formula group functions gsum/gcount/gavg/gmin/gmax('regex') aggregate
  over every context variable whose name matches the pattern, e.g.
  gsum('leaf_.*'). Adds string literals to the formula grammar and an
  IFormulaContext.ResolveMatching hook; GenomeContext enumerates matching
  genes, so a trait can sum/average a gene group.
- DefDatabase content patches: a { "type": "Patch", patches:[{ defType,
  match (regex on defName), set:{fields} }] } file sets fields on every
  matching raw def before resolution — mods patch Core in bulk.
- DefDatabase.RegisterValidator(typeKey, field, regex): load-time check
  that a string field matches a pattern, throwing otherwise (naming/format
  conventions).

Covered by FormulaTests (group aggregation, composition, bad calls) and
DefDatabaseTests (patch set/match/unknown-type, validator pass/reject).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/MrGameEng.Content/Genetics/Allele.cs

@@ -0,0 +1,16 @@
+namespace MrGameEng.Genetics;
+
+/// <summary>
+/// A diploid gene slot: the two allele values an individual carries for one gene. Stored as floats
+/// for both gene kinds — a <see cref="GeneKind.Discrete"/> gene simply holds integral variant
+/// indices. How the pair becomes a single phenotype value is decided by the gene's
+/// <see cref="GeneKind"/> (see <see cref="Genome.Express"/>).
+/// </summary>
+public readonly record struct Allele(float A, float B)
+{
+    /// <summary>The average of the two alleles — the phenotype of a numeric gene.</summary>
+    public float Mean => (A + B) * 0.5f;
+
+    /// <summary>The lower (dominant) of the two alleles — the phenotype of a discrete gene.</summary>
+    public float Dominant => MathF.Min(A, B);
+}

src/MrGameEng.Content/Genetics/GeneDef.cs

@@ -0,0 +1,97 @@
+using System.Text.Json.Serialization;
+using MrGameEng.Formulas;
+using MrGameEng.Mods;
+
+namespace MrGameEng.Genetics;
+
+/// <summary>How a gene's two alleles are stored and expressed into a phenotype value.</summary>
+public enum GeneKind
+{
+    /// <summary>A continuous value; the phenotype is the average of the two alleles (hybrid blending).</summary>
+    Numeric,
+
+    /// <summary>
+    /// A discrete allele index in <c>[0, Variants)</c>; the lower index is dominant, so the
+    /// phenotype is <c>min(a, b)</c> — a higher (recessive) variant shows only when homozygous.
+    /// A two-variant discrete gene is effectively a flag.
+    /// </summary>
+    Discrete,
+}
+
+/// <summary>
+/// An organism-agnostic gene definition — the unit the whole gene system is built from. A
+/// <see cref="GeneDef"/> describes how to generate an individual's two alleles, how they mutate
+/// when bred, and how the gene <see cref="Effects"/> contribute to named phenotype traits via
+/// <see cref="Formula"/> expressions. Nothing here is plant-, animal- or human-specific, so the
+/// same machinery drives any organism and arbitrary hybrids (a genome can carry any mix of genes).
+/// </summary>
+public sealed class GeneDef : Def
+{
+    /// <summary>Whether the gene is continuous or a discrete dominant/recessive allele.</summary>
+    public GeneKind Kind { get; init; } = GeneKind.Numeric;
+
+    /// <summary>Numeric: the central value an allele is generated around.</summary>
+    public float Default { get; init; }
+
+    /// <summary>Numeric: lower clamp for generated and mutated allele values.</summary>
+    public float Min { get; init; } = float.NegativeInfinity;
+
+    /// <summary>Numeric: upper clamp for generated and mutated allele values.</summary>
+    public float Max { get; init; } = float.PositiveInfinity;
+
+    /// <summary>Numeric: relative spread of generated alleles around <see cref="Default"/> (allele = Default ± Spread·|Default|).</summary>
+    public float Spread { get; init; }
+
+    /// <summary>Numeric: relative magnitude of a mutation step (value ± Magnitude·|value|).</summary>
+    public float MutationMagnitude { get; init; } = 0.1f;
+
+    /// <summary>Discrete: number of allele variants, valued <c>0..Variants-1</c>.</summary>
+    public int Variants { get; init; } = 2;
+
+    /// <summary>
+    /// Discrete: relative weights for generating each variant (length <see cref="Variants"/>).
+    /// Empty means a uniform distribution.
+    /// </summary>
+    public float[] VariantWeights { get; init; } = [];
+
+    /// <summary>Probability, per allele, that a mutation occurs when this gene is passed to a child.</summary>
+    public float MutationChance { get; init; }
+
+    /// <summary>
+    /// The gene's contributions to phenotype traits: trait name → formula. Each formula may use the
+    /// variable <c>value</c> (this gene's expressed phenotype), any other gene's id (its expressed
+    /// value) and any environment variable the caller supplies. Contributions to the same trait
+    /// across genes are summed.
+    /// </summary>
+    public Dictionary<string, string> Effects { get; init; } = new();
+
+    /// <summary>Free-form category tags for grouping genes (used by formula grouping and content tooling).</summary>
+    public string[] Tags { get; init; } = [];
+
+    private IReadOnlyDictionary<string, Formula>? _compiled;
+
+    /// <summary>The <see cref="Effects"/> compiled once into evaluable formulas (lazy, cached).</summary>
+    [JsonIgnore]
+    public IReadOnlyDictionary<string, Formula> CompiledEffects => _compiled ??= CompileEffects();
+
+    private Dictionary<string, Formula> CompileEffects()
+    {
+        var compiled = new Dictionary<string, Formula>(StringComparer.Ordinal);
+        foreach (var (trait, expression) in Effects)
+        {
+            try
+            {
+                compiled[trait] = Formula.Compile(expression);
+            }
+            catch (FormulaException error)
+            {
+                throw new InvalidDataException(
+                    $"Gene '{DefName}' effect on trait '{trait}' has an invalid formula "
+                        + $"\"{expression}\": {error.Message}"
+                );
+            }
+        }
+
+        return compiled;
+    }
+}

src/MrGameEng.Content/Genetics/GeneSampling.cs

@@ -0,0 +1,56 @@
+namespace MrGameEng.Genetics;
+
+/// <summary>
+/// Shared, deterministic allele sampling used by both <see cref="Genome.Generate"/> (gene defaults)
+/// and <see cref="GenomeTemplate"/> (per-individual base overrides). Centralizes the numeric
+/// spread+clamp and the weighted discrete pick so the two paths stay consistent.
+/// </summary>
+internal static class GeneSampling
+{
+    /// <summary>A numeric allele drawn as <c>baseValue ± spread·|baseValue|</c>, clamped to the gene's range.</summary>
+    public static float Numeric(GeneDef gene, float baseValue, float spread, Random random)
+    {
+        var value = baseValue + (random.NextSingle() * 2f - 1f) * spread * MathF.Abs(baseValue);
+        return Math.Clamp(value, gene.Min, gene.Max);
+    }
+
+    /// <summary>
+    /// A discrete variant index in <c>[0, Variants)</c>, picked from <paramref name="weights"/> when
+    /// they match the variant count, otherwise the gene's own weights, otherwise uniformly.
+    /// </summary>
+    public static float Variant(GeneDef gene, float[]? weights, Random random)
+    {
+        var variants = Math.Max(1, gene.Variants);
+        var w =
+            weights is { Length: > 0 } && weights.Length == variants
+                ? weights
+                : gene.VariantWeights;
+        if (w.Length != variants)
+        {
+            return random.Next(variants);
+        }
+
+        var total = 0f;
+        foreach (var value in w)
+        {
+            total += MathF.Max(0f, value);
+        }
+
+        if (total <= 0f)
+        {
+            return random.Next(variants);
+        }
+
+        var roll = random.NextSingle() * total;
+        for (var i = 0; i < variants; i++)
+        {
+            roll -= MathF.Max(0f, w[i]);
+            if (roll < 0f)
+            {
+                return i;
+            }
+        }
+
+        return variants - 1;
+    }
+}

src/MrGameEng.Content/Genetics/Genome.cs

@@ -0,0 +1,156 @@
+namespace MrGameEng.Genetics;
+
+/// <summary>
+/// An individual's managed genome: a variable-composition map from gene id to the
+/// <see cref="Allele"/> pair it carries. Because composition is open, two organisms need not share
+/// the same gene set and a genome can gain "foreign" genes — the basis for arbitrary hybrids. The
+/// genome is generated from a set of <see cref="GeneDef"/>s, bred meiotically with mutation, and
+/// expressed into phenotype values; all randomness flows through a caller-owned seeded
+/// <see cref="Random"/> so the simulation stays deterministic.
+/// </summary>
+public sealed class Genome
+{
+    private readonly Dictionary<string, Allele> _alleles;
+
+    /// <summary>Creates an empty genome.</summary>
+    public Genome() => _alleles = new Dictionary<string, Allele>(StringComparer.Ordinal);
+
+    /// <summary>Creates a genome from an existing allele map (copied).</summary>
+    public Genome(IReadOnlyDictionary<string, Allele> alleles) =>
+        _alleles = new Dictionary<string, Allele>(alleles, StringComparer.Ordinal);
+
+    /// <summary>The carried genes and their allele pairs.</summary>
+    public IReadOnlyDictionary<string, Allele> Alleles => _alleles;
+
+    /// <summary>Whether the genome carries the gene <paramref name="geneId"/>.</summary>
+    public bool Has(string geneId) => _alleles.ContainsKey(geneId);
+
+    /// <summary>Gets or sets the allele pair for <paramref name="geneId"/>.</summary>
+    public Allele this[string geneId]
+    {
+        get => _alleles[geneId];
+        set => _alleles[geneId] = value;
+    }
+
+    /// <summary>Removes a gene from the genome; returns whether it was present.</summary>
+    public bool Remove(string geneId) => _alleles.Remove(geneId);
+
+    /// <summary>
+    /// Expresses the gene's phenotype value: the mean of the alleles for a numeric gene, the
+    /// dominant (lower) allele for a discrete one. Throws if the genome does not carry the gene.
+    /// </summary>
+    public float Express(GeneDef gene)
+    {
+        if (!_alleles.TryGetValue(gene.DefName, out var allele))
+        {
+            throw new KeyNotFoundException($"Genome does not carry gene '{gene.DefName}'.");
+        }
+
+        return gene.Kind == GeneKind.Numeric ? allele.Mean : allele.Dominant;
+    }
+
+    /// <summary>Builds the allele map for serialization (a copy).</summary>
+    public Dictionary<string, Allele> ToDictionary() => new(_alleles, StringComparer.Ordinal);
+
+    /// <summary>
+    /// Generates a fresh genome carrying every gene in <paramref name="genes"/>, each allele drawn
+    /// independently around the gene's default with its spread (numeric) or from its variant
+    /// distribution (discrete).
+    /// </summary>
+    public static Genome Generate(IEnumerable<GeneDef> genes, Random random)
+    {
+        var genome = new Genome();
+        foreach (var gene in genes)
+        {
+            genome._alleles[gene.DefName] = new Allele(
+                GenerateAllele(gene, random),
+                GenerateAllele(gene, random)
+            );
+        }
+
+        return genome;
+    }
+
+    /// <summary>
+    /// Breeds a child genome from two parents (meiosis): the child carries every gene either parent
+    /// has. For a gene both carry, one allele is drawn from each parent; for a gene only one parent
+    /// carries, it is inherited (from that parent, on both sides) with 50% probability. Every
+    /// inherited allele may then mutate per its <see cref="GeneDef"/>. <paramref name="registry"/>
+    /// supplies the def for each gene id; genes absent from it are skipped.
+    /// <paramref name="mutationChance"/>, when given, overrides every gene's
+    /// <see cref="GeneDef.MutationChance"/> — letting the caller drive mutation from an evolvable
+    /// trait rather than a fixed per-gene constant.
+    /// </summary>
+    public static Genome Breed(
+        Genome a,
+        Genome b,
+        IReadOnlyDictionary<string, GeneDef> registry,
+        Random random,
+        float? mutationChance = null
+    )
+    {
+        var child = new Genome();
+        foreach (var geneId in UnionKeys(a, b))
+        {
+            if (!registry.TryGetValue(geneId, out var gene))
+            {
+                continue;
+            }
+
+            var chance = mutationChance ?? gene.MutationChance;
+            var inA = a.Has(geneId);
+            var inB = b.Has(geneId);
+            if (inA && inB)
+            {
+                child._alleles[geneId] = new Allele(
+                    Meiosis(gene, a[geneId], chance, random),
+                    Meiosis(gene, b[geneId], chance, random)
+                );
+            }
+            else if (random.NextSingle() < 0.5f)
+            {
+                var parent = inA ? a : b;
+                child._alleles[geneId] = new Allele(
+                    Meiosis(gene, parent[geneId], chance, random),
+                    Meiosis(gene, parent[geneId], chance, random)
+                );
+            }
+        }
+
+        return child;
+    }
+
+    // One inherited allele: pick one of the parent slot's two alleles, then maybe mutate it.
+    private static float Meiosis(GeneDef gene, Allele parent, float mutationChance, Random random)
+    {
+        var inherited = random.NextSingle() < 0.5f ? parent.A : parent.B;
+        if (random.NextSingle() >= mutationChance)
+        {
+            return inherited;
+        }
+
+        if (gene.Kind == GeneKind.Discrete)
+        {
+            return GeneSampling.Variant(gene, null, random);
+        }
+
+        var shifted =
+            inherited
+            + (random.NextSingle() * 2f - 1f) * gene.MutationMagnitude * MathF.Abs(inherited);
+        return Math.Clamp(shifted, gene.Min, gene.Max);
+    }
+
+    private static float GenerateAllele(GeneDef gene, Random random) =>
+        gene.Kind == GeneKind.Discrete
+            ? GeneSampling.Variant(gene, null, random)
+            : GeneSampling.Numeric(gene, gene.Default, gene.Spread, random);
+
+    // Deterministic union of both parents' gene ids (ordered) so breeding is reproducible.
+    private static IEnumerable<string> UnionKeys(Genome a, Genome b)
+    {
+        var keys = new SortedSet<string>(StringComparer.Ordinal);
+        keys.UnionWith(a._alleles.Keys);
+        keys.UnionWith(b._alleles.Keys);
+        return keys;
+    }
+}

src/MrGameEng.Content/Genetics/GenomeTemplate.cs

@@ -0,0 +1,61 @@
+namespace MrGameEng.Genetics;
+
+/// <summary>
+/// A species' (or any organism kind's) gene allotment: which <see cref="GeneDef"/>s an individual
+/// carries and the per-organism base values its alleles are generated around. The same
+/// <see cref="GeneDef"/> (e.g. "optimal light") is shared by every species, while the template
+/// supplies the species-specific centre and spread — so an oak and grass differ in values, not in
+/// machinery. <see cref="Generate"/> draws a fresh individual; <see cref="Registry"/> feeds breeding
+/// and trait computation.
+/// </summary>
+public sealed class GenomeTemplate
+{
+    /// <summary>
+    /// One gene in the allotment. <paramref name="Base"/>/<paramref name="Spread"/> centre a numeric
+    /// gene's alleles; <paramref name="VariantWeights"/> (optional) override a discrete gene's
+    /// variant distribution for this organism.
+    /// </summary>
+    public readonly record struct Entry(
+        GeneDef Gene,
+        float Base,
+        float Spread,
+        float[]? VariantWeights = null
+    );
+
+    private readonly List<Entry> _entries;
+    private readonly Dictionary<string, GeneDef> _registry;
+
+    /// <summary>Builds a template from its gene entries.</summary>
+    public GenomeTemplate(IEnumerable<Entry> entries)
+    {
+        _entries = entries.ToList();
+        _registry = new Dictionary<string, GeneDef>(StringComparer.Ordinal);
+        foreach (var entry in _entries)
+        {
+            _registry[entry.Gene.DefName] = entry.Gene;
+        }
+    }
+
+    /// <summary>The gene entries that make up the allotment.</summary>
+    public IReadOnlyList<Entry> Entries => _entries;
+
+    /// <summary>Gene id → def for every carried gene; pass to <see cref="Genome.Breed"/> and <see cref="Phenotype.Compute"/>.</summary>
+    public IReadOnlyDictionary<string, GeneDef> Registry => _registry;
+
+    /// <summary>Generates a fresh individual: two alleles per gene drawn around each entry's base/variant.</summary>
+    public Genome Generate(Random random)
+    {
+        var genome = new Genome();
+        foreach (var entry in _entries)
+        {
+            genome[entry.Gene.DefName] = new Allele(Draw(entry, random), Draw(entry, random));
+        }
+
+        return genome;
+    }
+
+    private static float Draw(Entry entry, Random random) =>
+        entry.Gene.Kind == GeneKind.Discrete
+            ? GeneSampling.Variant(entry.Gene, entry.VariantWeights, random)
+            : GeneSampling.Numeric(entry.Gene, entry.Base, entry.Spread, random);
+}

src/MrGameEng.Content/Genetics/Phenotype.cs

@@ -0,0 +1,87 @@
+using MrGameEng.Formulas;
+
+namespace MrGameEng.Genetics;
+
+/// <summary>
+/// Computes the trait layer — the phenotype the simulation actually reads — from a
+/// <see cref="Genome"/>. Each gene's <see cref="GeneDef.Effects"/> formulas are evaluated and their
+/// results summed per trait name, so systems never touch genes directly: one fruiting system reads
+/// a <c>fruitYield</c> trait whether it comes from a tree or a human carrying a "fruit" gene.
+/// Formulas see the variable <c>value</c> (the contributing gene's expressed phenotype), any other
+/// carried gene's id, and whatever environment variables the caller supplies.
+/// </summary>
+public static class Phenotype
+{
+    /// <summary>
+    /// Evaluates every carried gene's effects against the genome and an optional
+    /// <paramref name="environment"/>, summing contributions into a trait map. Genes missing from
+    /// <paramref name="registry"/> are skipped.
+    /// </summary>
+    public static Dictionary<string, float> Compute(
+        Genome genome,
+        IReadOnlyDictionary<string, GeneDef> registry,
+        IFormulaContext? environment = null
+    )
+    {
+        var traits = new Dictionary<string, float>(StringComparer.Ordinal);
+        var context = new GenomeContext(genome, registry, environment);
+        foreach (var geneId in genome.Alleles.Keys)
+        {
+            if (!registry.TryGetValue(geneId, out var gene) || gene.CompiledEffects.Count == 0)
+            {
+                continue;
+            }
+
+            context.Self = genome.Express(gene);
+            foreach (var (trait, formula) in gene.CompiledEffects)
+            {
+                traits[trait] = traits.GetValueOrDefault(trait) + formula.Evaluate(context);
+            }
+        }
+
+        return traits;
+    }
+
+    // Resolves formula variables for a gene effect: 'value' is the current gene's phenotype, any
+    // carried gene's id resolves to its phenotype, anything else falls through to the environment.
+    private sealed class GenomeContext(
+        Genome genome,
+        IReadOnlyDictionary<string, GeneDef> registry,
+        IFormulaContext? environment
+    ) : IFormulaContext
+    {
+        public float Self;
+
+        public float Resolve(string name)
+        {
+            if (name == "value")
+            {
+                return Self;
+            }
+
+            if (genome.Has(name) && registry.TryGetValue(name, out var gene))
+            {
+                return genome.Express(gene);
+            }
+
+            if (environment is not null)
+            {
+                return environment.Resolve(name);
+            }
+
+            throw new FormulaException($"Unknown variable '{name}' while computing traits.");
+        }
+
+        // Группировка генов в формулах: значения всех генов, чьи id подходят под шаблон (gsum/gavg/…).
+        public IEnumerable<float> ResolveMatching(Func<string, bool> matches)
+        {
+            foreach (var geneId in genome.Alleles.Keys)
+            {
+                if (matches(geneId) && registry.TryGetValue(geneId, out var gene))
+                {
+                    yield return genome.Express(gene);
+                }
+            }
+        }
+    }
+}

src/MrGameEng.Content/Mods/DefDatabase.cs

@@ -1,5 +1,6 @@
 using System.Text.Json;
 using System.Text.Json.Nodes;
+using System.Text.RegularExpressions;
 
 namespace MrGameEng.Mods;
 
@@ -24,6 +25,18 @@ public sealed class DefDatabase
     private readonly Dictionary<string, TypeEntry> _byKey = new(StringComparer.OrdinalIgnoreCase);
     private readonly Dictionary<Type, TypeEntry> _byType = [];
 
+    /// <summary>Reserved def-file <c>"type"</c> that carries content patches rather than defs.</summary>
+    public const string PatchTypeKey = "Patch";
+
+    private sealed record PatchRule(string DefType, Regex Match, JsonObject Set);
+
+    private sealed record ValidationRule(string Field, Regex Pattern, string Description);
+
+    private readonly List<PatchRule> _patches = [];
+    private readonly Dictionary<string, List<ValidationRule>> _validators = new(
+        StringComparer.OrdinalIgnoreCase
+    );
+
     private static readonly JsonDocumentOptions DocumentOptions = new()
     {
         CommentHandling = JsonCommentHandling.Skip,
@@ -43,6 +56,38 @@ public sealed class DefDatabase
         _byType.Add(typeof(T), entry);
     }
 
+    /// <summary>
+    /// Registers a load-time validation: the string <paramref name="field"/> of every resolved def of
+    /// type <paramref name="typeKey"/> must match <paramref name="pattern"/> (a regex), or
+    /// <see cref="Load"/> throws. Non-string or absent fields are skipped. Use it to enforce naming
+    /// conventions (e.g. gene ids start with <c>Gene</c>) or key/format rules across a mod's content.
+    /// </summary>
+    public void RegisterValidator(
+        string typeKey,
+        string field,
+        string pattern,
+        string? description = null
+    )
+    {
+        Regex regex;
+        try
+        {
+            regex = new Regex(pattern, RegexOptions.CultureInvariant);
+        }
+        catch (ArgumentException error)
+        {
+            throw new ArgumentException($"Invalid validator regex '{pattern}': {error.Message}");
+        }
+
+        if (!_validators.TryGetValue(typeKey, out var list))
+        {
+            list = [];
+            _validators[typeKey] = list;
+        }
+
+        list.Add(new ValidationRule(field, regex, description ?? $"pattern /{pattern}/"));
+    }
+
     /// <summary>
     /// Loads every <c>Defs/**/*.json</c> of <paramref name="mods"/> (in load order) and
     /// resolves inheritance. Call once after registering all def types.
@@ -66,6 +111,8 @@ public sealed class DefDatabase
             }
         }
 
+        ApplyPatches();
+
         foreach (var entry in _byKey.Values)
         {
             Resolve(entry);
@@ -133,6 +180,12 @@ public sealed class DefDatabase
             ?? throw new InvalidDataException(
                 $"Def file '{file}' (mod '{mod.Id}') has no \"type\" field."
             );
+        if (string.Equals(typeKey, PatchTypeKey, StringComparison.OrdinalIgnoreCase))
+        {
+            LoadPatches(mod, file, root);
+            return;
+        }
+
         if (!_byKey.TryGetValue(typeKey, out var entry))
         {
             throw new InvalidDataException(
@@ -169,8 +222,83 @@ public sealed class DefDatabase
         }
     }
 
-    private static void Resolve(TypeEntry entry)
+    // Парсит файл-патч: операции { defType, match (регэксп по defName), set: {поля} }.
+    private void LoadPatches(Mod mod, string file, JsonNode root)
     {
+        if (root["patches"] is not JsonArray patches)
+        {
+            throw new InvalidDataException(
+                $"Patch file '{file}' (mod '{mod.Id}') has no \"patches\" array."
+            );
+        }
+
+        foreach (var node in patches)
+        {
+            if (node is not JsonObject patch)
+            {
+                throw new InvalidDataException(
+                    $"Patch file '{file}' (mod '{mod.Id}') contains a non-object patch."
+                );
+            }
+
+            var defType =
+                patch["defType"]?.GetValue<string>()
+                ?? throw new InvalidDataException($"A patch in '{file}' has no \"defType\".");
+            var match =
+                patch["match"]?.GetValue<string>()
+                ?? throw new InvalidDataException($"A patch in '{file}' has no \"match\".");
+            if (patch["set"] is not JsonObject set)
+            {
+                throw new InvalidDataException($"A patch in '{file}' has no \"set\" object.");
+            }
+
+            Regex regex;
+            try
+            {
+                regex = new Regex(match, RegexOptions.CultureInvariant);
+            }
+            catch (ArgumentException error)
+            {
+                throw new InvalidDataException(
+                    $"Patch in '{file}' has invalid regex '{match}': {error.Message}"
+                );
+            }
+
+            _patches.Add(new PatchRule(defType, regex, (JsonObject)set.DeepClone()));
+        }
+    }
+
+    // Применяет патчи к сырым дефам (до резолва), в порядке загрузки: каждому дефу нужного типа,
+    // чьё имя подходит под регэксп, проставляются поля set. Поля наследуются детьми как обычно.
+    private void ApplyPatches()
+    {
+        foreach (var patch in _patches)
+        {
+            if (!_byKey.TryGetValue(patch.DefType, out var entry))
+            {
+                throw new InvalidDataException(
+                    $"A patch targets unknown def type '{patch.DefType}'."
+                );
+            }
+
+            foreach (var raw in entry.Raw)
+            {
+                if (!patch.Match.IsMatch(raw.Key))
+                {
+                    continue;
+                }
+
+                foreach (var (key, value) in patch.Set)
+                {
+                    raw.Value[key] = value?.DeepClone();
+                }
+            }
+        }
+    }
+
+    private void Resolve(TypeEntry entry)
+    {
+        _validators.TryGetValue(entry.Key, out var rules);
         foreach (var defName in entry.Raw.Keys.Order(StringComparer.Ordinal))
         {
             var merged = MergeChain(entry, defName, []);
@@ -179,6 +307,11 @@ public sealed class DefDatabase
                 continue;
             }
 
+            if (rules is not null)
+            {
+                Validate(entry.Key, defName, merged, rules);
+            }
+
             var def =
                 (Def?)merged.Deserialize(entry.ClrType, ModInfo.JsonOptions)
                 ?? throw new InvalidDataException(
@@ -188,6 +321,28 @@ public sealed class DefDatabase
         }
     }
 
+    private static void Validate(
+        string typeKey,
+        string defName,
+        JsonObject merged,
+        List<ValidationRule> rules
+    )
+    {
+        foreach (var rule in rules)
+        {
+            if (
+                merged[rule.Field] is JsonValue value
+                && value.TryGetValue<string>(out var text)
+                && !rule.Pattern.IsMatch(text)
+            )
+            {
+                throw new InvalidDataException(
+                    $"Def '{defName}' ({typeKey}) field '{rule.Field}'=\"{text}\" violates {rule.Description}."
+                );
+            }
+        }
+    }
+
     private static JsonObject MergeChain(TypeEntry entry, string defName, HashSet<string> seen)
     {
         if (!seen.Add(defName))

src/MrGameEng.Content/Mods/ModInfo.cs

@@ -1,4 +1,5 @@
 using System.Text.Json;
+using System.Text.Json.Serialization;
 
 namespace MrGameEng.Mods;
 
@@ -14,6 +15,7 @@ public sealed class ModInfo
         ReadCommentHandling = JsonCommentHandling.Skip,
         AllowTrailingCommas = true,
         WriteIndented = true,
+        Converters = { new JsonStringEnumConverter() },
     };
 
     /// <summary>Unique mod id, referenced by <see cref="Dependencies"/> of other mods.</summary>

src/MrGameEng.Core/Formulas/FormulaContext.cs

@@ -12,6 +12,13 @@ public interface IFormulaContext
     /// if the name is unknown — the engine does not invent a default.
     /// </summary>
     float Resolve(string name);
+
+    /// <summary>
+    /// Returns the values of every variable whose name satisfies <paramref name="matches"/> — the
+    /// backing for the group functions (<c>gsum</c>, <c>gavg</c>, …) that aggregate over a name
+    /// pattern, e.g. all <c>leaf_*</c> genes. Contexts with no enumerable variables return nothing.
+    /// </summary>
+    IEnumerable<float> ResolveMatching(Func<string, bool> matches) => [];
 }
 
 /// <summary>An <see cref="IFormulaContext"/> backed by a lookup delegate — handy for tests and ad-hoc use.</summary>

src/MrGameEng.Core/Formulas/FormulaGroups.cs

@@ -0,0 +1,98 @@
+using System.Text.RegularExpressions;
+using Node = System.Func<MrGameEng.Formulas.IFormulaContext, float>;
+
+namespace MrGameEng.Formulas;
+
+/// <summary>
+/// The group functions — <c>gsum</c>, <c>gcount</c>, <c>gavg</c>, <c>gmin</c>, <c>gmax</c> — which
+/// aggregate over every context variable whose name matches a regex literal, e.g.
+/// <c>gsum('leaf_.*')</c> sums all <c>leaf_*</c> genes. The pattern is a string literal compiled to a
+/// <see cref="Regex"/> once at parse time; aggregation reads <see cref="IFormulaContext.ResolveMatching"/>.
+/// </summary>
+internal static class FormulaGroups
+{
+    private static readonly HashSet<string> Names = new(StringComparer.Ordinal)
+    {
+        "gsum",
+        "gcount",
+        "gavg",
+        "gmin",
+        "gmax",
+    };
+
+    public static bool IsGroupFunction(string name) => Names.Contains(name);
+
+    public static Node Build(string name, string pattern)
+    {
+        Regex regex;
+        try
+        {
+            regex = new Regex(pattern, RegexOptions.CultureInvariant);
+        }
+        catch (ArgumentException error)
+        {
+            throw new FormulaException($"Invalid regex '{pattern}': {error.Message}");
+        }
+
+        bool Match(string variable) => regex.IsMatch(variable);
+        return name switch
+        {
+            "gsum" => ctx => Aggregate(ctx.ResolveMatching(Match), sum: true),
+            "gavg" => ctx => Aggregate(ctx.ResolveMatching(Match), average: true),
+            "gcount" => ctx => Count(ctx.ResolveMatching(Match)),
+            "gmin" => ctx => Extreme(ctx.ResolveMatching(Match), max: false),
+            "gmax" => ctx => Extreme(ctx.ResolveMatching(Match), max: true),
+            _ => throw new FormulaException($"Unknown group function '{name}'."),
+        };
+    }
+
+    private static float Aggregate(
+        IEnumerable<float> values,
+        bool sum = false,
+        bool average = false
+    )
+    {
+        var total = 0f;
+        var count = 0;
+        foreach (var value in values)
+        {
+            total += value;
+            count++;
+        }
+
+        if (average)
+        {
+            return count == 0 ? 0f : total / count;
+        }
+
+        return total; // sum (count==0 → 0)
+    }
+
+    private static float Count(IEnumerable<float> values)
+    {
+        var count = 0;
+        foreach (var _ in values)
+        {
+            count++;
+        }
+
+        return count;
+    }
+
+    private static float Extreme(IEnumerable<float> values, bool max)
+    {
+        var has = false;
+        var best = 0f;
+        foreach (var value in values)
+        {
+            if (!has || (max ? value > best : value < best))
+            {
+                best = value;
+            }
+
+            has = true;
+        }
+
+        return best; // empty → 0
+    }
+}

src/MrGameEng.Core/Formulas/FormulaLexer.cs

@@ -6,6 +6,7 @@ internal enum TokenType
 {
     Number,
     Identifier,
+    String,
     Plus,
     Minus,
     Star,
@@ -99,6 +100,27 @@ internal static class FormulaLexer
                 continue;
             }
 
+            if (c == '\'')
+            {
+                var open = i;
+                var start = ++i;
+                while (i < source.Length && source[i] != '\'')
+                {
+                    i++;
+                }
+
+                if (i >= source.Length)
+                {
+                    throw new FormulaException($"Unterminated string at position {open}.");
+                }
+
+                tokens.Add(
+                    new Token(TokenType.String, open, text: source.Substring(start, i - start))
+                );
+                i++; // пропускаем закрывающую кавычку
+                continue;
+            }
+
             var pos = i;
             switch (c)
             {

src/MrGameEng.Core/Formulas/FormulaParser.cs

@@ -232,6 +232,20 @@ internal sealed class FormulaParser(List<Token> tokens)
     private Node ParseCall(string name)
     {
         Expect(TokenType.LParen);
+        if (FormulaGroups.IsGroupFunction(name))
+        {
+            var pattern = Current;
+            if (!Match(TokenType.String))
+            {
+                throw new FormulaException(
+                    $"Group function '{name}' expects a quoted regex pattern at position {pattern.Position}."
+                );
+            }
+
+            Expect(TokenType.RParen);
+            return FormulaGroups.Build(name, pattern.Text);
+        }
+
         var args = new List<Node>();
         if (!Peek(TokenType.RParen))
         {

tests/MrGameEng.Content.Tests/Genetics/GeneDefLoadTests.cs

@@ -0,0 +1,68 @@
+using MrGameEng.Genetics;
+using MrGameEng.Mods;
+using Xunit;
+
+namespace MrGameEng.Genetics.Tests;
+
+/// <summary>
+/// Verifies <see cref="GeneDef"/> loads through the real <see cref="DefDatabase"/> the way the game
+/// loads <c>genes.json</c>: string-named <see cref="GeneKind"/>, parent inheritance and effect maps.
+/// </summary>
+public sealed class GeneDefLoadTests : IDisposable
+{
+    private readonly string _root = Directory.CreateTempSubdirectory("mrge-gene-tests-").FullName;
+
+    public void Dispose() => Directory.Delete(_root, recursive: true);
+
+    private DefDatabase Load(string defsJson)
+    {
+        var modDir = Path.Combine(_root, "mod");
+        Directory.CreateDirectory(Path.Combine(modDir, "Defs"));
+        File.WriteAllText(Path.Combine(modDir, "Defs", "genes.json"), defsJson);
+        var database = new DefDatabase();
+        database.RegisterType<GeneDef>("Gene");
+        database.Load([new Mod(new ModInfo { Id = "mod" }, modDir)]);
+        return database;
+    }
+
+    [Fact]
+    public void Load_NumericGeneWithParentAndEffects_Resolves()
+    {
+        var database = Load(
+            """
+            { "type": "Gene", "defs": [
+                { "defName": "BaseGene", "abstract": true, "spread": 0.1, "mutationChance": 0.05 },
+                { "defName": "GeneVigor", "parent": "BaseGene", "default": 1.0, "min": 0.1, "max": 3.0,
+                  "tags": ["growth"], "effects": { "vigor": "value" } }
+            ]}
+            """
+        );
+
+        var gene = database.Get<GeneDef>("GeneVigor");
+        Assert.Equal(GeneKind.Numeric, gene.Kind);
+        Assert.Equal(0.1f, gene.Spread); // inherited from parent
+        Assert.Equal(0.05f, gene.MutationChance); // inherited
+        Assert.Equal(3.0f, gene.Max);
+        Assert.Equal(["growth"], gene.Tags);
+        Assert.Equal("value", gene.Effects["vigor"]);
+        Assert.Single(gene.CompiledEffects); // formula compiles
+    }
+
+    [Fact]
+    public void Load_DiscreteKindByName_Parses()
+    {
+        var database = Load(
+            """
+            { "type": "Gene", "defs": [
+                { "defName": "GeneMorph", "kind": "Discrete", "variants": 2,
+                  "variantWeights": [0.8, 0.2], "effects": { "variant": "value" } }
+            ]}
+            """
+        );
+
+        var gene = database.Get<GeneDef>("GeneMorph");
+        Assert.Equal(GeneKind.Discrete, gene.Kind);
+        Assert.Equal(2, gene.Variants);
+        Assert.Equal([0.8f, 0.2f], gene.VariantWeights);
+    }
+}

tests/MrGameEng.Content.Tests/Genetics/GeneticsTests.cs

@@ -0,0 +1,194 @@
+using MrGameEng.Formulas;
+using MrGameEng.Genetics;
+using Xunit;
+
+namespace MrGameEng.Genetics.Tests;
+
+public class GeneticsTests
+{
+    private static GeneDef Numeric(
+        string name,
+        float def,
+        float spread = 0f,
+        float min = float.NegativeInfinity,
+        float max = float.PositiveInfinity,
+        float mutationChance = 0f,
+        float mutationMagnitude = 0.1f,
+        Dictionary<string, string>? effects = null
+    ) =>
+        new()
+        {
+            DefName = name,
+            Kind = GeneKind.Numeric,
+            Default = def,
+            Spread = spread,
+            Min = min,
+            Max = max,
+            MutationChance = mutationChance,
+            MutationMagnitude = mutationMagnitude,
+            Effects = effects ?? new(),
+        };
+
+    private static GeneDef Discrete(string name, int variants = 2, float mutationChance = 0f) =>
+        new()
+        {
+            DefName = name,
+            Kind = GeneKind.Discrete,
+            Variants = variants,
+            MutationChance = mutationChance,
+        };
+
+    private static Dictionary<string, GeneDef> Registry(params GeneDef[] genes) =>
+        genes.ToDictionary(g => g.DefName, g => g, StringComparer.Ordinal);
+
+    [Fact]
+    public void Generate_NumericAlleles_StayWithinSpreadAndClamp()
+    {
+        var gene = Numeric("vigor", def: 1f, spread: 0.2f, min: 0f, max: 2f);
+        var random = new Random(7);
+
+        for (var i = 0; i < 200; i++)
+        {
+            var genome = Genome.Generate([gene], random);
+            var allele = genome["vigor"];
+            Assert.InRange(allele.A, 0.8f, 1.2f);
+            Assert.InRange(allele.B, 0.8f, 1.2f);
+        }
+    }
+
+    [Fact]
+    public void Generate_SameSeed_IsDeterministic()
+    {
+        var genes = new[] { Numeric("a", 1f, 0.3f), Discrete("morph", 2) };
+
+        var first = Genome.Generate(genes, new Random(42));
+        var second = Genome.Generate(genes, new Random(42));
+
+        Assert.Equal(first["a"], second["a"]);
+        Assert.Equal(first["morph"], second["morph"]);
+    }
+
+    [Fact]
+    public void Express_Numeric_IsAlleleMean()
+    {
+        var gene = Numeric("opt", 0f);
+        var genome = new Genome { ["opt"] = new Allele(0.4f, 0.8f) };
+
+        Assert.Equal(0.6f, genome.Express(gene), 5);
+    }
+
+    [Fact]
+    public void Express_Discrete_DominantIsLowerIndex()
+    {
+        var gene = Discrete("morph", 2);
+
+        Assert.Equal(0f, new Genome { ["morph"] = new Allele(0f, 1f) }.Express(gene)); // heterozygous → dominant 0
+        Assert.Equal(1f, new Genome { ["morph"] = new Allele(1f, 1f) }.Express(gene)); // homozygous recessive
+    }
+
+    [Fact]
+    public void Breed_WithoutMutation_InheritsOneAlleleFromEachParent()
+    {
+        var gene = Numeric("g", 0f, mutationChance: 0f);
+        var registry = Registry(gene);
+        var a = new Genome { ["g"] = new Allele(1f, 2f) };
+        var b = new Genome { ["g"] = new Allele(3f, 4f) };
+
+        var child = Genome.Breed(a, b, registry, new Random(1));
+
+        Assert.Contains(child["g"].A, new[] { 1f, 2f }); // first allele from parent a
+        Assert.Contains(child["g"].B, new[] { 3f, 4f }); // second allele from parent b
+    }
+
+    [Fact]
+    public void Breed_UnionOfGenes_ProducesHybridComposition()
+    {
+        // a carries only "leaf", b carries only "root" — a child can carry both (hybrid).
+        var registry = Registry(Numeric("leaf", 1f), Numeric("root", 1f));
+        var a = new Genome { ["leaf"] = new Allele(1f, 1f) };
+        var b = new Genome { ["root"] = new Allele(2f, 2f) };
+
+        var carriedBoth = false;
+        for (var seed = 0; seed < 50 && !carriedBoth; seed++)
+        {
+            var child = Genome.Breed(a, b, registry, new Random(seed));
+            carriedBoth = child.Has("leaf") && child.Has("root");
+        }
+
+        Assert.True(carriedBoth, "single-parent genes should sometimes both be inherited");
+    }
+
+    [Fact]
+    public void Breed_HighMutation_DiscreteCanFlipVariant()
+    {
+        var gene = Discrete("morph", variants: 2, mutationChance: 1f);
+        var registry = Registry(gene);
+        var parent = new Genome { ["morph"] = new Allele(0f, 0f) };
+
+        var sawOne = false;
+        for (var seed = 0; seed < 50 && !sawOne; seed++)
+        {
+            var child = Genome.Breed(parent, parent, registry, new Random(seed));
+            var allele = child["morph"];
+            sawOne = allele.A == 1f || allele.B == 1f;
+        }
+
+        Assert.True(sawOne, "with full mutation a 0/0 parent should sometimes yield variant 1");
+    }
+
+    [Fact]
+    public void Compute_GeneEffect_UsesValueVariable()
+    {
+        var gene = Numeric("vigor", 0f, effects: new() { ["growth"] = "value * 2" });
+        var genome = new Genome { ["vigor"] = new Allele(1.5f, 2.5f) }; // mean 2
+
+        var traits = Phenotype.Compute(genome, Registry(gene));
+
+        Assert.Equal(4f, traits["growth"], 5); // 2 * 2
+    }
+
+    [Fact]
+    public void Compute_MultipleGenes_SumContributionsPerTrait()
+    {
+        var a = Numeric("a", 0f, effects: new() { ["yield"] = "value" });
+        var b = Numeric("b", 0f, effects: new() { ["yield"] = "value" });
+        var genome = new Genome { ["a"] = new Allele(3f, 3f), ["b"] = new Allele(4f, 4f) };
+
+        var traits = Phenotype.Compute(genome, Registry(a, b));
+
+        Assert.Equal(7f, traits["yield"], 5);
+    }
+
+    [Fact]
+    public void Compute_FormulaReadsEnvironmentAndOtherGenes()
+    {
+        var opt = Numeric("optLight", 0.5f);
+        var vigor = Numeric(
+            "vigor",
+            1f,
+            effects: new() { ["rate"] = "value * (1 - abs(light - optLight))" }
+        );
+        var genome = new Genome
+        {
+            ["optLight"] = new Allele(0.5f, 0.5f),
+            ["vigor"] = new Allele(1f, 1f),
+        };
+        var env = new DelegateFormulaContext(n =>
+            n == "light" ? 0.7f : throw new FormulaException(n)
+        );
+
+        var traits = Phenotype.Compute(genome, Registry(opt, vigor), env);
+
+        Assert.Equal(0.8f, traits["rate"], 5); // 1 * (1 - |0.7 - 0.5|)
+    }
+
+    [Fact]
+    public void CompiledEffects_InvalidFormula_ThrowsWithGeneAndTrait()
+    {
+        var gene = Numeric("bad", 0f, effects: new() { ["t"] = "value *" });
+
+        var error = Assert.Throws<InvalidDataException>(() => _ = gene.CompiledEffects);
+        Assert.Contains("bad", error.Message);
+        Assert.Contains("t", error.Message);
+    }
+}

tests/MrGameEng.Content.Tests/Genetics/GenomeTemplateTests.cs

@@ -0,0 +1,106 @@
+using MrGameEng.Genetics;
+using Xunit;
+
+namespace MrGameEng.Genetics.Tests;
+
+public class GenomeTemplateTests
+{
+    private static GeneDef Numeric(string name, float min, float max) =>
+        new()
+        {
+            DefName = name,
+            Kind = GeneKind.Numeric,
+            Min = min,
+            Max = max,
+        };
+
+    private static GeneDef Discrete(string name, int variants = 2) =>
+        new()
+        {
+            DefName = name,
+            Kind = GeneKind.Discrete,
+            Variants = variants,
+        };
+
+    [Fact]
+    public void Generate_UsesPerEntryBaseAndSpread_NotGeneDefault()
+    {
+        var gene = Numeric("opt", min: 0f, max: 100f); // GeneDef.Default is 0
+        var template = new GenomeTemplate([
+            new GenomeTemplate.Entry(gene, Base: 50f, Spread: 0.1f),
+        ]);
+        var random = new Random(3);
+
+        for (var i = 0; i < 200; i++)
+        {
+            var allele = template.Generate(random)["opt"];
+            Assert.InRange(allele.A, 45f, 55f); // around the template base, not 0
+            Assert.InRange(allele.B, 45f, 55f);
+        }
+    }
+
+    [Fact]
+    public void Generate_TwoSpecies_DifferInCentre()
+    {
+        var gene = Numeric("opt", 0f, 100f);
+        var oak = new GenomeTemplate([new GenomeTemplate.Entry(gene, 20f, 0f)]);
+        var grass = new GenomeTemplate([new GenomeTemplate.Entry(gene, 80f, 0f)]);
+
+        Assert.Equal(20f, oak.Generate(new Random(1)).Express(gene), 3);
+        Assert.Equal(80f, grass.Generate(new Random(1)).Express(gene), 3);
+    }
+
+    [Fact]
+    public void Registry_CoversEntries_AndDrivesBreeding()
+    {
+        var template = new GenomeTemplate([
+            new GenomeTemplate.Entry(Numeric("a", 0f, 10f), 5f, 0.1f),
+            new GenomeTemplate.Entry(Discrete("morph"), 0f, 0f),
+        ]);
+        var random = new Random(9);
+        var a = template.Generate(random);
+        var b = template.Generate(random);
+
+        var child = Genome.Breed(a, b, template.Registry, random);
+
+        Assert.True(child.Has("a"));
+        Assert.True(child.Has("morph"));
+    }
+
+    [Fact]
+    public void Breed_MutationChanceOverride_ForcesMutation()
+    {
+        var gene = Numeric("a", min: -100f, max: 100f);
+        var registry = new Dictionary<string, GeneDef> { ["a"] = gene };
+        var parent = new Genome { ["a"] = new Allele(10f, 10f) };
+
+        // Override chance to 1 → every inherited allele mutates away from 10.
+        var moved = false;
+        for (var seed = 0; seed < 30 && !moved; seed++)
+        {
+            var child = Genome.Breed(
+                parent,
+                parent,
+                registry,
+                new Random(seed),
+                mutationChance: 1f
+            );
+            moved = child["a"].A != 10f || child["a"].B != 10f;
+        }
+
+        Assert.True(moved, "with overridden mutationChance=1 the allele should mutate");
+    }
+
+    [Fact]
+    public void Breed_MutationChanceZero_KeepsAlleles()
+    {
+        var gene = Numeric("a", -100f, 100f);
+        var registry = new Dictionary<string, GeneDef> { ["a"] = gene };
+        var parent = new Genome { ["a"] = new Allele(10f, 10f) };
+
+        var child = Genome.Breed(parent, parent, registry, new Random(5), mutationChance: 0f);
+
+        Assert.Equal(10f, child["a"].A);
+        Assert.Equal(10f, child["a"].B);
+    }
+}

tests/MrGameEng.Content.Tests/Mods/DefDatabaseTests.cs

@@ -143,4 +143,73 @@ public sealed class DefDatabaseTests : IDisposable
         Assert.Throws<KeyNotFoundException>(() => database.Get<AnimalDef>("Dodo"));
         Assert.False(database.TryGet<AnimalDef>("Dodo", out _));
     }
+
+    private Mod WriteMod(string fileName, string json)
+    {
+        var id = $"mod{_modCounter++:D2}";
+        var modDir = Path.Combine(_root, id);
+        Directory.CreateDirectory(Path.Combine(modDir, "Defs"));
+        File.WriteAllText(Path.Combine(modDir, "Defs", fileName), json);
+        return new Mod(new ModInfo { Id = id }, modDir);
+    }
+
+    [Fact]
+    public void Patch_SetsFields_OnDefsMatchingNamePattern()
+    {
+        var defs = WriteDefsMod(
+            """
+            { "type": "Animal", "defs": [
+                { "defName": "Wolf", "speed": 9 },
+                { "defName": "WolfPup", "speed": 4 },
+                { "defName": "Bear", "speed": 6 }
+            ]}
+            """
+        );
+        var patch = WriteMod(
+            "patches.json",
+            """{ "type": "Patch", "patches": [ { "defType": "Animal", "match": "Wolf.*", "set": { "legs": 6 } } ] }"""
+        );
+
+        var database = LoadAnimals(defs, patch);
+
+        Assert.Equal(6, database.Get<AnimalDef>("Wolf").Legs); // matched
+        Assert.Equal(6, database.Get<AnimalDef>("WolfPup").Legs); // matched
+        Assert.Equal(4, database.Get<AnimalDef>("Bear").Legs); // unmatched → default
+    }
+
+    [Fact]
+    public void Patch_UnknownDefType_Throws()
+    {
+        var patch = WriteMod(
+            "patches.json",
+            """{ "type": "Patch", "patches": [ { "defType": "Ghost", "match": ".*", "set": {} } ] }"""
+        );
+
+        Assert.Throws<InvalidDataException>(() => LoadAnimals(patch));
+    }
+
+    [Fact]
+    public void Validator_RejectsField_NotMatchingPattern()
+    {
+        var database = new DefDatabase();
+        database.RegisterType<AnimalDef>("Animal");
+        database.RegisterValidator("Animal", "defName", "^[A-Z]");
+        var bad = WriteDefsMod("""{ "type": "Animal", "defs": [ { "defName": "wolf" } ] }""");
+
+        var error = Assert.Throws<InvalidDataException>(() => database.Load([bad]));
+        Assert.Contains("wolf", error.Message);
+    }
+
+    [Fact]
+    public void Validator_Passes_WhenFieldMatches()
+    {
+        var database = new DefDatabase();
+        database.RegisterType<AnimalDef>("Animal");
+        database.RegisterValidator("Animal", "defName", "^[A-Z]");
+        database.Load([
+            WriteDefsMod("""{ "type": "Animal", "defs": [ { "defName": "Wolf", "speed": 7 } ] }"""),
+        ]);
+
+        Assert.Equal(7f, database.Get<AnimalDef>("Wolf").Speed);
+    }
 }

tests/MrGameEng.Core.Tests/FormulaTests.cs

@@ -109,4 +109,66 @@ public class FormulaTests
         var formula = Formula.Compile("x + 1");
         Assert.Throws<FormulaException>(() => formula.Evaluate());
     }
+
+    // --- Group functions (regex aggregation over matching variables) ---
+
+    private sealed class GroupContext(Dictionary<string, float> values) : IFormulaContext
+    {
+        public float Resolve(string name) => values[name];
+
+        public IEnumerable<float> ResolveMatching(Func<string, bool> matches)
+        {
+            foreach (var (name, value) in values)
+            {
+                if (matches(name))
+                {
+                    yield return value;
+                }
+            }
+        }
+    }
+
+    [Fact]
+    public void Evaluate_GroupFunctions_AggregateMatchingVariables()
+    {
+        var ctx = new GroupContext(
+            new()
+            {
+                ["leaf_a"] = 2f,
+                ["leaf_b"] = 4f,
+                ["leaf_c"] = 6f,
+                ["root_a"] = 100f,
+            }
+        );
+
+        Assert.Equal(12f, Formula.Compile("gsum('leaf_.*')").Evaluate(ctx), 4); // 2+4+6
+        Assert.Equal(3f, Formula.Compile("gcount('leaf_.*')").Evaluate(ctx), 4);
+        Assert.Equal(4f, Formula.Compile("gavg('leaf_.*')").Evaluate(ctx), 4);
+        Assert.Equal(2f, Formula.Compile("gmin('leaf_.*')").Evaluate(ctx), 4);
+        Assert.Equal(6f, Formula.Compile("gmax('leaf_.*')").Evaluate(ctx), 4);
+    }
+
+    [Fact]
+    public void Evaluate_GroupFunction_ComposesWithArithmetic()
+    {
+        var ctx = new GroupContext(new() { ["g1"] = 3f, ["g2"] = 5f });
+        Assert.Equal(16f, Formula.Compile("gsum('g.*') * 2").Evaluate(ctx), 4); // (3+5)*2
+    }
+
+    [Fact]
+    public void Evaluate_GroupFunction_NoMatches_IsZero()
+    {
+        var ctx = new GroupContext(new() { ["x"] = 1f });
+        Assert.Equal(0f, Formula.Compile("gsum('none_.*')").Evaluate(ctx), 4);
+        Assert.Equal(0f, Formula.Compile("gavg('none_.*')").Evaluate(ctx), 4);
+    }
+
+    [Theory]
+    [InlineData("gsum(leaf)")] // pattern must be a quoted string
+    [InlineData("gsum('[')")] // invalid regex
+    [InlineData("gsum('a' 'b')")] // extra token
+    public void Compile_BadGroupCall_Throws(string expr)
+    {
+        Assert.Throws<FormulaException>(() => Formula.Compile(expr));
+    }
 }