+URI, +Options)Register Prefix as an abbreviation for URI. Options:
true, replace existing namespace alias. Please note that
replacing a namespace is dangerous as namespaces affect preprocessing.
Make sure all code that depends on a namespace is compiled after
changing the registration.
true and Alias is already defined, keep the original
binding for Prefix and succeed silently.
Without options, an attempt to redefine an alias raises a permission
Predefined prefixes are: