Elements in lxml have asourceline attribute, but it is alwaysNone in trees parsed with html5lib.

html5lib also appears tokeep track of source line numbers for error messages.

I’d like to connect the two so that WeasyPrint can do its own error reporting based on line numbers of HTML elements. It seems like the attribute should be setin etree_lxml.py, but I don’t know how to access the input stream from there.

Suggestions?