Not for function keys in particular not for the modifiers. Just take a look at the output of 'infocmp' between your favorite terminal and your favorite terminal with tmux running in it or even just a different terminal itself.

Another issue is knowing capabilities, total number of colors, allowed attributes, default state of attributes, allowed actions when certain attributes are enabled or disabled.

There's about half of the definitions which are common across almost all modern terminals, and the other half are unique and describe unique implementation details of the emulator.