Node:Completion, Next:, Previous:Top, Up:Top



Completion

Apart from real-time validation, the most important feature that nxml-mode provides for assisting in document creation is "completion". Completion assists the user in inserting characters at point, based on knowledge of the schema and on the contents of the buffer before point.

The traditional GNU Emacs key combination for completion in a buffer is M-<TAB>. However, many window systems and window managers use this key combination themselves (typically for switching between windows) and do not pass it to applications. It's hard to find key combinations in GNU Emacs that are both easy to type and not taken by something else. C-<RET> (i.e. pressing the Enter or Return key, while the Ctrl key is held down) is available. It won't be available on a traditional terminal (because it is indistinguishable from Return), but it will work with a window system. Therefore we adopt the following solution by default: use C-<RET> when there's a window system and M-<TAB> when there's not. In the following, I will assume that a window system is being used and will therefore refer to C-<RET>.

Completion works by examining the symbol preceding point. This is the symbol to be completed. The symbol to be completed may be the empty. Completion considers what symbols starting with the symbol to be completed would be valid replacements for the symbol to be completed, given the schema and the contents of the buffer before point. These symbols are the possible completions. An example may make this clearer. Suppose the buffer looks like this (where -!- indicates point):

<html xmlns="http://www.w3.org/1999/xhtml">
<h-!-

and the schema is XHTML. In this context, the symbol to be completed is h. The possible completions consist of just head. Another example, is

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<-!-

In this case, the symbol to be completed is empty, and the possible completions are base, isindex, link, meta, script, style, title. Another example is:

<html xmlns="-!-

In this case, the symbol to be completed is empty, and the possible completions are just http://www.w3.org/1999/xhtml.

When you type C-<RET>, what happens depends on what the set of possible completions are.