The hxaddid command copies an HTML or XML file to standard output, while adding element IDs to the specified elements or classes.
For example, given the input
<p>A paragraph without an ID</p>
<p id="a-paragraph">A paragraph without an ID</p>
If you specify a class using .class then IDs will only be added to elements that contain that class. And if you specify an element and a class using elem.class then IDs will only be added to the specified elements that contain the specified class.
If two elements would naturally generate the same ID, a number is added to the ID name (starting with 0) to make sure the IDs are unique. IDs are not added to matching elements that already contain an ID.
hxaddid tries first to generate "readable" IDs, by forming the ID out of the letters and digits found in the content of the element and falls back to generating arbitrary IDs if it doesn't find enough. However, the algorithm in this version is primitive and only gives reasonable results for ASCII letters and digits.
Remote files (specified with a URL) are currently only supported for HTTP. Password-protected files or files that depend on HTTP "cookies" are not handled. (You can use tools such as curl(1) or wget(1) to retrieve such files.)