I agree with the value of this request, but it's just a start. There are so many ways data might be manipulated -- if we had the functions to do so -- that it makes me wonder how far MC might be evolved in this direction. I'd love to see it go FAAAAR -- Lotus Notes is a good example of a massive collection of string and number manipulation tools, since it's a rich-text "database" system. (In fact, I saw an impressive MC-type music library/player application built with Lotus Notes years ago -- just as a trade show demo of the product's app-development capabilities.) But with the focus on making MC a TV system, maybe extending its "language" isn't a goal.
Perhaps Matt or Jim or someone could one day tell us the vision or plan for providing more functions and expression capabilities, or not, whatever might be the case. Then we'd know whether to pile on the requests, or not. (I'd be happy to paste in some of the key Lotus Notes functions that I wish were in MC, things like searching right and left, frontward or backward, selecting by character count OR by a specified substring, and several more.)
My biggest wish is that a function or expression could be associated with every field (standard and custom) that gets executed when the field value is changed -- essentially a transformation that helps standardize the data every time it is saved. This would allow for such actions as forcing all caps for a field, or removing leading/trailing spaces, or even pushing a value into another field based on the changed field. Again, Lotus Notes is my model though many programmable systems allow this.
For instance, I find typing or pasting errors that resulted in Name or other field values with leading or dangling spaces, inadvertent but a problem for sorting and matching. If an an expression could be associated with the field to execute the Remove functions, the data could always be trimmed as desired, even after sloppy typing.
Or... If providing full expression execution per field is beyond the scope of MC, perhaps allow certain common actions to be controlled per field via checkboxes, actions like trimming leading/trailing spaces, forcing all-caps or lowercase or proper case, etc. It would be important that such a feature be available in both standard and custom fields.