It would be really nice to be able to define our own unique variables for any given task. I'll give you an example. Lets say that I am taking notes from a book that I am reading. Every entry gets a tag to indicate the page number like p26, p27, etc. This only helps me in a search if I separately list each page number that I'm looking for. But, if I could create a "page" variable, and designate the data type as an integer, then I could end up doing a search like

list:book and tag:place and page:"> 7" and page:"< 40"

to search for all book items from pages 8 through 39 that have the tag "place"

There are infinite useful ways that this feature could be used , and because it is such an advanced feature that would confuse many beginning RTM users, I think it is a feature that should only be offered to Pro Users. I plan to become a Pro user very soon, as soon as I get my next paycheck!