Non-Optional html5lib-modern introduces non-optional lxml dependency, defeats optional LXML.

[ashleysommer]

html5lib used to be an optional dependency in RDFLib (installed with the extra named rdflib[html]).

When replacing it with html5lib-modern, I ran some tests with it installed and without, and I noticed there are a bunch of RDFLib tests that fail if html5lib is not installed. Loading any literal with datatype xsd:html causes a very complicated code path that ends with a runtime error, when html5lib is not installed. So I changed it to non-optional, html5lib-modern is always installed as a dependency of RDFLib, and there is no [html] extra anymore in RDFLib 7.1.0.

However I just noticed that html5lib (and html5lib-modern) both depend on lxml. And lxml is an Optional dependency in RDFLib (some users don't want that overhead). So I suppose thats why html5lib was optional too.