[racket] Text% efficiently iterating over items

Is there a fast way to iterate over items or words in a text% instance
starting from some position. For example, I'd like to go forward or
backward starting from a position until a character in a given
srfi14 char-set is found. 

Using a string returned get-text doesn't seem to work in general because
of the ambiguity between "." meaning dot or being an embedded image.

Do I need to iterate over snips using find-snip and then use the same
position in the snip if it is a text-snip%? Is the position within a
text-snip% the same as the position used by find-snip? If not, how do I
calculate the offset?


Best,

Erich