Boolean properties must not be deleted but set

Deletion introduced bugs in some engines (no suprise)
Element#remove
cont. Element#remove
-- whitespace
Element#exclude and Element#include
Basic function and method for Text

Specifcally:
Text.isText
Text.validText
Text#exclude
Text#include
Text#remove
Node.validNode
Element#append
Element#prepend
Element#before
Element#after
Element#replace