public String ensureDefinitionKeyIsPlain(String definitionKey) {
        return definitionKey
                // avoid dollar symbols for inner types
                .replaceAll("\\$", "-")
                // marking arrays with three dots instead of square brackets
                .replaceAll("\\[\\]", "...")
                // indicating generics in underscores instead of angled brackets
                .replaceAll("[<>]", "_")
                // use dots instead of commas between type parameters
                .replaceAll(",", ".")
                // removing white-spaces and any other remaining invalid characters
                .replaceAll("[^a-zA-Z0-9\\.\\-_]+", "");
    }
Replace characters in the given definition key that are neither alphanumeric nor a dot, dash or underscore (as expected by OpenAPI).

@param definitionKey {@code SchemaDefinitionNamingStrategy} output
@return simplified version of the given definition key
jsonschema-generator/src/main/java/com/github/victools/jsonschema/generator/impl/SchemaCleanUpUtils.java