Smartsite 7 - ...

As of now, the sxml editor renders as a simple textarea.

Smarsite 7.3+

As of Smartsite 7.3 and later, Code Mirror is used as text editor.

Code Mirror example

Code Mirror is a versatile text editor implemented in Javascript which works in every browser. It features syntax highlighting, (tag) autocompletion, bracket and tag matching, etcetera.

Using the Ctrl-Space key combination, it even features a list of autocompletion hints for e.g. html attributes, dependent on the language (html, css, javascript).
Pressing F11 will toggle the editor into full screen mode.

The difference between the SxmlEditor control and the CodeMirror control, is that the SxmlEditor control includes schema validation support.