public static ScriptEnvironment<FeaturePostMatch> description(Root root) {
      return ProcessFeature.description(root)
        .forInput(FeaturePostMatch.class)
        .withDeclarations(
          Decls.newVar(MATCH_KEY, Decls.String),
          Decls.newVar(MATCH_VALUE, Decls.Any)
        );
    }
Context available after a feature has been matched.
<p>
Adds {@code match_key} and {@code match_value} variables that capture which tag key/value caused the feature to be
included.

@param parent    The parent context
@param matchKeys Keys that triggered the match
planetiler-custommap/src/main/java/com/onthegomap/planetiler/custommap/Contexts.java