Note that clap::App has been deprecated in favor of clap::Command. This has only one lifetime parameter ’help. Looking at where it’s used, this appears to be the lifetime of the help text that clap can emit, as all of the methods to add new flags and such take Into<&’help str>. In the case where these are hard-coded into the program, I’d expect ’help == ‘static.
Basically, the structure is declared to hold references of the form &’a… and &’b… embedded in it somewhere, presumably inside a container that starts empty. The actual value of these lifetimes don’t have to be determined at object creation time, but can instead be inferred by the compiler when methods are called that involve them.
As I can’t find any documentation or source code for the version with two lifetime parameters, I can’t say any more about what they represent. Probably, one of them serves the same purpose as ’help in the current version of clap.