Not really sure what you are looking for. Number of charcters between the first instance of the word and the second? If so you could use the position command to look for the text in a field or variable and use the occurence to determine which iteration you are looking for.
Position ( text ; searchString ; start ; occurrence )
So it could look something like
Position ( text ; searchString ; start ; 2) - Position ( text ; searchString ; start ; 1 )
Anyway, I have the FileMaker Missing manual APP. They were giving this away at one point. I did a search on the word proximety but came up with 0 results. So was unable to track down the section you were looking at.
Sorry, I'm not sure this is much help
It would be the searching within a user specified number of words between search string.
As an example: Dog and House with a proximity of 3, would return the results Dog House, House of Dog, Dog the house, etc.
I like your idea; perhaps modified for words instead of characters it would be good.
That sounds like a custom function might be of help. The book has a section on Custom functions what you were reading might be in that section. Also check Brian Dunning's web site. http://www.brianduning.com
Best of luck