What information should I include in a letter of support for a grant? What are the key information that should be included in a letter of support on a grant application? What information should I avoid?

I'm a theorist and I am planning to list my expertise and experience in similar problems. But I don't know how to convey that I would actually support the project if funded.
A good letter of support, in my mind, should:


Convey a clear understanding of the proposal in question;
Demonstrate that the letter writer is in a position to support the application—in other words, she has the requisite experience to contribute;
Clearly indicate what the writer will do to support the grant in the event it gets funded.


I recently contributed such a letter for an educational grant. I cited my research, which was a fit for the program; and conveyed support for the program as the academic administrator of a summer program as well as a mentor in that same program. I also clearly conveyed my intention to support the program by directly mentoring a program fellow.