attributeVisitor = function (node) {
      if (!astUtil.isClassAttribute(node, classRegex) || skipClassAttribute) {
        return;
      }
      if (astUtil.isLiteralAttributeValue(node)) {
        parseForShorthandCandidates(node);
      } else if (node.value && node.value.type === 'JSXExpressionContainer') {
        parseForShorthandCandidates(node, node.value.expression);
      }
    }
Parse the classnames and report found shorthand candidates
@param {ASTNode} node The root node of the current parsing
@param {ASTNode} arg The child node of node
@returns {void}