This section describes a number of basic concepts, which will be used again and again in the following descriptions. Most of it should be familiar to EMACS users. New users are advised not to get stuck reading this section, because most of the information will become clear the first time you play with the editor on a computer.

Screen Layout

ce divides the screen into two areas. The bottom-most line on the screen, which is used to display messages and ask one line questions, is called the echo line. Typing in the echo line is like typing commands to the operating system. More details later in the section The Echo Line.

The remainder of the screen is filled with text windows . When ce is first started, there will be one or two more windows, depending on how many files you specify on the invocation line. If there is only one window, it fills the screen. If there are two or more windows, each window occupies an equal share of the screen. Windows can be created, deleted, and adjusted in size using ce commands.

Mode Lines

The last line of a window (the line, usually in reverse video, that starts with CrystalEdit) is the mode line for the window. It contains information about what is being displayed in the window. Mode lines separate windows from each other and from the echo line.

Four important bits of information are displayed in the mode line. These are:

• the buffer changed flag (either a * or blank)
• the buffer mode (if any) in parentheses
• the buffer name
• the file name

A window is always displaying a buffer. The name of the buffer being displayed in the window is shown in the mode line, right after the CrystalEdit and the buffer mode (if any).

A buffer may have a file associated with it. Usually this is the last file read into or written from the buffer. If a file is associated with the buffer, the name of the file is displayed in the mode line, prefixed by File:.

ce knows if a buffer has been changed since it was last written to its associated file. It informs you of this fact by displaying a * in the mode line immediately to the left of the CrystalEdit string.

Keyboard Conventions

Internally, ce represents keyboard characters in a special 31 bit code. This code consists of 21 bits of character data (ASCII plus Unicode), and 3 flags: the CONTROL flag, the META flag, and the CTLX flag. Combinations of the three flags are possible, with the exception that META and CTLX cannot be set at the same time.

This manual represents 31 bit keycodes in a standard way. If you have a character A, then that character with the CONTROL bit set is written as C-A. That character with the META bit set is written as M-A. That character with the CTLX bit set is written as C-X A. If both the META and CONTROL bits are set, it is written as M-C-A. If both the CTLX and CONTROL bits are set, it is written as C-X C-A.

Characters with the flag bits set are entered by prefixing the desired character with another character, as follows:

• To get a character with the CONTROL bit set, hold down the CTRL key while entering the character. An alternative method is to prefix the character with Control-^ (the word Control here, and in the next few examples, means the key marked Control or CTRL on the ASCII keyboard).

• To get a character with the META bit set, prefix the character with Control-[, Escape, or ESC. An alternative method that works on a PC keyboard is hold down the ALT key while entering the character; this works only with ALT-A through ALT-Z.

• To get a character with the CTLX bit set, prefix the character with Control-X.

• To get a character with the CONTROL and META bits set, prefix the character with Control-\. An alternative method is to prefix the character with ESC, then hold down CTRL while entering the character.

CONTROL characters are very important, so there is a shorthand way of typing them, as follows:

• Characters between Control-@ (Control-Space on some keyboards) and Control-Z are mapped to the characters @ through Z with the CONTROL bit set.

• Characters between Control-a and Control-z are mapped to the characters A through Z with the CONTROL bit set.

This shorthand means that that M-C-V, for example, can be entered either as ESC followed by Control-V, or as Control-\ followed by V. As another example, C-X C-B is entered as Control-X followed by Control-B.

The PC Keyboard

ce understands all of the cursor keypad and function keys on a typical keyboard. These keys include the function keys (F1-F12), cursor keys (Up, Down, Left, Right, PgUp, PgDn, Home, End), Delete, and Insert.

You can use the ALT key as the META flag, instead of the ESC key. For example, the M-L command (lower-word) can be executed in either of two ways:

• Hit ESC followed by L.

• Hold down ALT and hit L.

The ALT key only works with alphabetic characters (A through Z). Using ALT and CTRL together is also not supported.

Key Bindings

Normally when you type a key, ce attempts to interprets the key as a command. Internally, ce keeps a table of each possible key, and the command assocated with that key. This association is called the "key binding." Even text keys, such as the letters, numbers, and punctuation, are "bound" to a command called "ins-self" that just inserts the key that invoked it into the text.

Not all commands are bound to a particular key. These commands can still be entered by using the (M-X) (ESC X) "extended-command" prefix.

See the Quick Start section of this manual for a list of the predefined key bindings.

In this guide, the command descriptions will give not only the key that the command is normally bound to, but also the command name, which is useful when you want to use that command in a Ruby extension.

The Echo Line

The echo line has two purposes; displaying messages and asking one line questions.

Two types of messages are displayed in the echo line. Informational messages tell you something useful, but do not imply in any way that something is wrong. These messages are always enclosed in square brackets ([ and ]). Error messages indicate that something has prevented a command from being executed. They are never enclosed in square brackets, and will be accompanied by a beep from the terminal's bell if the sound of the bell is not too obnoxious.

The echo line is cleared by the next keystroke.

The echo line is also used for asking and answering questions. After the prompt, you can type any characters you like. The reply is always terminated by a Return. Before you commit to the reply, you can edit the reply using the following characters:

• Backspace or Rubout: delete the character to the left of the cursor.

• Control-A: move the cursor to the beginning of the line.

• Control-B: move the cursor one character to the left.

• Control-D: delete the character under the cursor.

• Control-E: move the cursor to end of the line.

• Control-F: move the cursor one character to the right.

• Control-K: delete from the cursor to the end of the line.

• Control-U: delete the entire line.

You can also abort the command in progress by typing Control-G. Command processors are designed to ask all questions before doing nasty things, so that you will never do damage by aborting a command.

The echo line supports autocompletion. If you are entering a command name, a filename, or a buffer name, you can use the Tab key to tell ce to complete as much of the entry as possible, based on what you have entered so far. Pressing the the Tab key twice in a row will open a new temporary window containing the list of possible choices.

If you are entering a search string, pressing Control-S will fill in the previous search string.

Command Arguments

All commands can be given a numeric argument. Most commands use this argument as a repeat count. Commands can tell if an argument has been supplied, and will use a default argument if no user argument is present. Usually, the default argument is 1.

A C-U preceding a command always introduces an argument.

If a numeric argument is just a string of C-U characters, then the value of the argument is 4^(number of C-U characters), where "^" means "to the power." Therefore C-U is 4, C-U C-U is 16, C-U C-U C-U is 64, and so on. Some commands care if an argument is present, but don't look at its value; the C-U character is a good way to say "here is an argument".

If there is a signed decimal number after the string of C-U characters it specifies the value of the argument. In this case the number of C-U characters does not matter. An argument of 10 can be represented by C-U 10, C-U C-U 10, or even C-U C-U C-U C-U 10.

Dot, Mark, and the Region

Most editing commands act on the character or characters surrounding the current location in the current buffer. The thing that marks the current location is always called dot . The dot always points between two characters. This isn't the way that the cursor works on most display terminals, so, by convention, dot is always immediately to the left of the character on which the hardware cursor is placed.

There is also a second remembered position in the buffer, called the mark . There are commands that set the value of mark.

Some commands act on a block of text called the region . The region is all of the characters between dot and mark. The relative positions of dot and mark do not matter.