src/vs/editor/contrib/snippet/browser/snippetParser.ts/Variable/resolve
class Variable:	resolve(resolver: VariableResolver): boolean {
		let value = resolver.resolve(this);
		if (this.transform) {
			value = this.transform.resolve(value || '');
		}
		if (value !== undefined) {
			this._children = [new Text(value)];
			return true;
		}
		return false;
	}