The jed editor has several hundred built–in functions as well as many
more written in the S-Lang extension language. Many of these functions
are bound to keys and many are not. It is simply unreasonable to require
the user to remember if a function is bound to a key or not and, if it is,
to remember the key to which it is bound. This is especially true of those
functions that are bound but rarely used. More often than not, one simply
forgets the exact name or spelling of a function and requires a little
help. For this reason, jed supports command line completion in the
mini-buffer. This function, called emacs_escape_x, is bound to the
key ESC X. This is one binding that must be remembered!
As an example, suppose that you are editing several buffers and you wish
to insert the contents of one buffer into the current buffer. The
function that does this is called insert_buffer and has no default
key-binding. Pressing ESC X produces the prompt M-x. This
prompt, borrowed from the Emacs editor, simply means that ESC X
was pressed. Now type in and hit the space bar or the TAB
key. In this context (completion context) the space bar and the TAB
will expand the string in the Mini-Buffer up until it is no longer unique.
In this case, insert_file and insert_buffer are only the two
functions that start with in. Hence, in will expand to
insert_ at which point it becomes necessary to enter more
information to uniquely specify the desired function. However, in a
completion context, the space bar also has a special property that enables
the user to cycle among the possible completions. For this example,
hitting the space bar twice consecutively will produce the string
insert_file and hitting it again produces the desired string
insert_buffer.
The role of the space bar in completion is a point where Emacs and jed
differ. Emacs will pop up a buffer of possible completions but jed expects
the user to press the space bar to cycle among them. Both have there pros
and cons. Frequently, one sees messages on the Usenet newsgroup
gnu.emacs.help from Emacs users asking for the kind of completion
jed employs.