function visitor( node, state, c ) {
			var FLG = ( node !== state.ancestors[ state.ancestors.length-1 ] );
			if ( FLG ) {
				state.ancestors.push( node );
			}
			clbk( node, state, c ); // eslint-disable-line node/callback-return
			if ( FLG ) {
				state.ancestors.pop();
			}
		}
Callback invoked upon encountering an AST node.

@private
@param {Node} node - AST node
@param {Object} state - state
@param {Function} c - callback