itemscope should be supported as a boolean attribute.

for reference, schema.org has been pushing it as such (https://schema.org/docs/gs.html#microdata_itemscope_itemtype)

running something through the Tokenizer/Sanitizer will set it to an empty attribute

input: <article itemscope>
output: <article itemscope="">

it looks like this can be handled by editing constants.py and doing the following to enable it on all tags:

booleanAttributes = {
-    "": frozenset(["irrelevant"]),
+    "": frozenset(["irrelevant", "itemscope"]),