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	MicroGnuEmacs Termcap Terminal Capabilities

The termcap library needs to know where to get the terminal type and
termcap capibilities file from.  UNIX and Os9/68k users should "setenv
TERM" to their terminal type, and "setenv TERMCAP" if they are using a
non-standard termcap file.  VMS users should see AAAREADME.1ST for
information on how to define the logical names TERM and ETC to point
to the termcap definition file.  Users of other operating systems
should do the aproprate thing.  For an example of a termcap file, UNIX
users may look in /etc/termcap, Os9/68k users may look at
/dd/sys/termcap (if present), and VMS users should see the file
[.SYS.VMS.TERMCAP]TERMCAP. 

MicroGnuEmacs requires that certain terminal capabilities exist in the
specified termcap entry.  The "cm" (cursor motion) capability *must*
be available to use MicroGnuEmacs.  (Yes, it is possible to fake cm
with some other capibilities, but MicroGnuEmacs doesn't try.)  If your
terminal is one that uses control characters in the paramater portion
of the "cm" string, the "up" and "bc" capabilites may also be needed.
(See your termlib documentation for when this is so.)

If the following capabilities are available, they are used.  The AL
and DL sequences are not totally standard, but having them improves
the performance of the editor, since it doesn't have to redraw the
screen to delete a line.  They should not be used if they need control
characters as paramaters.

	cd	-- clear display
	ce	-- clear to eol

	al	-- insert 1 line
	dl	-- delete 1 line

	AL	-- parametrized insert line (note capitalization)
	DL	-- parametrized delete line (note capitalization)

	ti	-- cursor movement initialization string
	te	-- cursor movement end string

The cs capability is not as standard as some of the other
capibilities, but is used by MicroGnuEmacs when available.  It is used
to define a "scrolling region", which defines a window within the
screen where all the action takes place.  A newline character at the
bottom of this area scrolls the rest of the text in the area up one
line, just like the normal screen; a reverse linefeed (sr) at the top
of the window moves all the text in the area down a line.
MicroGnuEmacs does not properly handle "cs" if your terminal needs
control characters as paramaters, and in this case "cs" should not be
defined.  

If the cs and sr capabilities are available, the termcap driver uses
these to make the insert/delete line functions work more smoothly. If
only the cs capability is present, it is still used for the delete
line function, but not for inserting lines.

The definition of the cs capability is: the first parameter in the
sequence defines the first row (origin 0) that is in the scrolling
region, and the second argument defines the last row to include in the
scrolling region.

	cs	-- set scrolling region (arg1 = top, arg2 = bottom)
	sr	-- reverse index

The following capabilities provide for an enhanced (reverse-video
or otherwise rendered) mode line.  The sg entry should not be present
on terminals that do this to characters as they are placed on the
screen.  Terminals that	put a region of the screen in the standout
mode should have sg defined as numeric: :sg#0: for terminals that do
this on regions but don't take any character positions to do this,
(this may be a non-standard interprition of the meaning of sg) and the
number of character positions taken by any other terminal.

	so	-- enter standout mode
	se	-- leave standout mode
	sg	-- number of character positions used by standout

			Function Keys

If MicroGnuEmacs is compiled with XKEYS defined, a new feature of the
termcap driver is support for function keys, based on the termcap
entry that defines the terminal.  This may not be be deisriable in all
cases, especially those in which the terminal in use does not use ESC
as the first character of all arrow and function keys.  If you do
deside to use this feature, don't expect it to work with all terminal
types.  Those termial types it doesn't work with will have to use
modified termcaps that do not include the termcap sequences described
below to be useful with MicroGnuEmacs compiled with the XKEYS option. 
XKEYS also interferes with the proper operation of delayed prompts.

The termcap "standard" provides for a number of sequences that define
how to activate the function keys, what the function key sequences
are, and the names of the function keys.  The termcap driver uses the
following capabilities to parse for function key sequences:

	ks	-- start using function keys
	ke	-- finish using the function keypad
	kh	-- home key
	ku	-- up arrow
	kd	-- down arrow
	kl	-- left arrow
	kr	-- right arrow
	k0-k9	-- standard termcap function keys (1-10)
	l0-l9	-- labels for same

The following key capabilities are not standard, but are used if
they are in the termcap:

	K0-K9	-- function keys 10 through 19
	L0-L9	-- labels for same

For example, the DEC LK201 (vt200-series, VAXstation) keyboard has an
editing keypad. A VT200 termcap entry could include the following
capabilities to go into application keypad mode, set up the arrow keys,
and map the editing keypad to internal function key codes KF0-KF7:

	...the beginning of the termcap entry....
	:ks=\E[?1h\E=:ke=\E[?1l\E>:\
	:ku=\EOA:kd=\EOB:kr=\EOC:kl=\EOD:kh=\E[H:\
	:k0=\E[28~:l0=Help:\
	:k1=\E[29~:l1=Do:\
	:k2=\E[1~:l2=Find:\
	:k3=\E[2~:l3=Insert Here:\
	:k4=\E[3~:l4=Remove:\
	:k5=\E[4~:l5=Select:\
	:k6=\E[5~:l6=Prev Screen:\
	:k7=\E[6~:l7=Next Screen:\

There is one problem with supporting function keys: If the META
introducer key (usually ESC) is used as the initial character of a
function key sequence, how is the parser to know when the user intends
the introducer to be taken at face value?  The parser doesn't have
enough information.

The approach the current code takes is that if the META introducer is
the first character in a function sequence, and the second character c
isn't part of a function key sequence, the parser returns (KMETA | c).
If it sees *two* META introducers in a row, it returns one instance of
METACH. This approach is subject to discussion and debate, but it
works right most of the time.
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