in gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/Graph.java [1000:1007]
default boolean supportsVariables() {
return supportsBooleanValues() || supportsByteValues() || supportsDoubleValues() || supportsFloatValues()
|| supportsIntegerValues() || supportsLongValues() || supportsMapValues()
|| supportsMixedListValues() || supportsSerializableValues()
|| supportsStringValues() || supportsUniformListValues() || supportsBooleanArrayValues()
|| supportsByteArrayValues() || supportsDoubleArrayValues() || supportsFloatArrayValues()
|| supportsIntegerArrayValues() || supportsLongArrayValues() || supportsStringArrayValues();
}