Lispworks also does not accept surrogate characters.

[Yehouda]

Currently on LispWorks it fails to compile becaus eof an error inputstream.lisp, the same as on abcl, ccl and mezzano. Need to add lispworks to the conditionalization inside the value of invalid-unicode (line 299 of the current code):

#-(or abcl ccl mezzano lispworks) ,@`(

Probably even better to implement the suggestion in https://github.com/rotatef/cl-html5-parser/issues/7.