Where are special system words like MISSING listed (and what they do)?

[ohrenkino]

@dec

i mean, under 'FILTERS'????

Yes, just as has been revealed to you in your own thread:

Logical Operators ... Blank etc

i can't find any operators for things like ifblank, ifchar, ifnumeric, and such so, for example, how do i test for a blank tag field? this is obviously a very useful/important test

And these keywords only work in filters not application-wide.