Making phrases in text invisible / visible on a display

List,

I'm looking for a way to make text (phrases thereof) in a display  
invisible / visible without changing the underlying string. Like for  
example with an emphasis value #invisible similiar to the existing ones  
#(normal bold italic narrow underlined struckOut). The effect should be  
that #invisible emphasized portions of text are *automagically* collapsed  
to zero width on the display (and/or perhaps an alternate / placeholder  
symbol is shown instead of the collapsed).

Is there already something into that direction which can be reused.

If not and anyways: pointers, comments and suggestions all appreciated.

Thank you in advance.

/Klaus