Unnecessary Memory Usage in Parser in XF
Under XenForo, the parser instantiates another copy of itself to build a list of tags to apply properties to. The only problem is, we are already in the parser, so we don't need the list of tags first. I believe this code was here to build the tag list for the admin form that allows admins to edit the tag properties, but we certainly don't need to generate that list on every page load.
Further, the function in question has a goldfish's memory. Rather than storing the results for later use, it repeatedly rebuilds the list every time an operation is performed through the Tag model.