Ashley Sanders writes:
>> Here's my use case:
>> 
>>   foo.fileName =/substring=-5 .html
>> 
>> Find all filenames that end in '.html', which can't otherwise be
>> accomplished unless you can start a number of characters back from
>> the end.
> 
> If that's why you want, then why not create an operator or modifier
> such as "ends-with", rather than creating an obscure and error prone
> substring modifier?

That's pretty much what Rob has done, except that instead of a limited
"ends-with" modifier, he's made a more general "count backwards from
the end" modifier.  And it is spelled "-".  Any cosmetic resemblance
to negative numbers should be ignored: the use of the "-" character is
arbitrary.  In fact, we could use (say) "$" instead, like this:

	foo.fileName =/substring=$5 .html

So that all of the string except the first and last characters would
be written:

	foo.fileName =/substring=2,$1 ark_side_of_the_moo

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