code: function isString(node, literal) {
  	if ( node == null || node.type !== Syntax.Literal || typeof node.value !== "string" ) {
  		return false;
  	}
  	return literal == null ? true : node.value === literal;
  }
docs: Checks whether the given node is a string literal.
  
  If second parameter 'literal' is given, the value of the node is additionally compared with that literal.
  
  @private
  @param {ESTree} node
  @param {string} [literal]
  @returns {boolean} Whether the node is a literal and whether its value matches the given string