Termcap/Terminfo question

[ok at quintus]

When should a program use the 'is' (initialisation string) or 'if'
(initialisation file) capabilities?  I have a program which sends this
string when it starts, but a number of VT100 emulators adapt to window
size by adding appropriate co#COLS and li#ROWS information, but leave
is: setting the scrolling region to 24 lines, which seems unhelpful.

There seem to be three sets of strings a program might send at start
and finish:
	is/rs	initialisation string / reset string
		[is1..is3/rs1..rs3 in terminfo; also if/rf]

	vs/ve	"visual" start / "visual" end

	ti/te	said to be meant for things that use cm (cursor motion)

Exactly when should these things be used?

Is there a book which explains in clear and simple language what each of
the capabilities means, how to decide what to set it to, and when to use it?
[I have the 5R3 manuals.  I need an idiot's guide.]