Possible to store a variable in one comp and accessible to all other comps.

Hi There,

This question is mainly for architectural reasons.  Is there a way within the After Effects project file, to declare a global variable that is accessible to all comps?  I want to simply define a variable, set its value, and have that variable accessible to all the comps in the project.  Is there an "order" to which expressions get evaluated first?

Any pointers or tips are greatly appreciated.

Thanks!