Check if a runtime value looks like an Expression.
Expressions in the externally tagged format are single-key objects whose
key is one of the variants generated from Rust's Expression enum.
Checking the exact variant registry prevents one-field payload structs such
as { this: expression } from being exposed as phantom expression nodes.
DataType's own data_type discriminator also matches an Expression variant:
{ data_type: 'date' } is a descriptor, whereas the expression envelope is
{ data_type: { data_type: 'date' } }.
AST Module
This module provides types, type guards, helpers, and visitor utilities for working with SQL AST nodes.
Query builders are in
src/builders.ts(WASM-backed).