WebCopy has a fixed set of rules which govern how it crawls a document such as a HTML page or style sheet for additional resources. With the rise of responsive websites, these default rules might not always be sufficient - for example custom data attributes may be applied to the img tag in order to support retina images. WebCopy allows you to specify additional attributes to scan, either by using simple names or more complex XPath expressions.
For more advanced scenarios, you can use XPath expressions. For example, if a document contained a p tag and an img tag, each with a custom attribute named data-original, you can scan only those on the img tag by using the expression //img/@data-original.
Enter only one attribute name per line
WebCopy does not currently support custom attributes where multiple URLs are contained in a single attribute, or the attribute value includes additional content around the URL.