Unicode input

I've been exploring some MathML. MathML has a large entity set for 
mathematical symbols, but I'm also looking at marking up directly in 
unicode using utf-8 encoding rather than using the entities.

Any suggestions as to what to use as a "MathML input method" for XEmacs? 
I've seen the x-symbol package and the "Tex input method", just 
wondering if there are others.

So far I've been using insert-ucs-character to directly input unicode 
points. But I seem to recall an input method/approach where the unicode 
character could be typed in the buffer as a four digit hex number and it 
would be converted. Is there such?