Debra Cameron - Learning GNU Emacs, 3rd Edition

Table 8-7. Nxml mode commands

Lennart Stafflin's psgml mode has been around for a while. It is more robust than Emacs's own SGML mode, but, like any add-on, you have to install it in order to use it. Either install TEI Emacs as described earlier or download psgml mode from http://www.lysator.liu.se/projects/about_psgml.html and follow the installation instructions there. TEI Emacs includes a functioning psgml mode, so if you've installed TEI Emacs, your setup work is done.

psgml mode consists of two parts: sgml-mode for writing SGML and xml-mode for writing XML (and in our case XHTML).

To start psgml mode to edit our XHTML file, type M-x xml-mode.

XML appears on the mode line and an *SGML LOG*window opens. If you are using TEI Emacs, XSLT appears on the mode line along with XML.

The *SGML LOG*window displays messages about this session. (If it doesn't appear immediately, click on the first character in the file.) The log buffer complains that it could not find an external entity called html. This file has been changed to work with the XHTML RELAX NG schema. psgml mode expects it to conform to an XHTML DTD. To get started with the (minimal) work needed to undertake the transformation from a schema-based file to a DTD-based file, we ask psgml to normalize the buffer.

Type: M-x sgml-normalizeor select Normalize from the Modify menu

psgml mode eliminates the namespace declaration in the tag.

More needs to be done, however. The first statements in an XHTML file include an XML statement and a DOCTYPE entry that identifies the DTD this document should be validated against. One of the nice things about TEI Emacs is that it includes a variety of DTDs. (Users of standard psgml mode don't have this feature; sorry. [52])

At the beginning of the file, select DTD → Insert DTD → XHTML Transitional.

Emacs inserts the two required elements for us.

That's all it takes to make this file a well-formed XHTML file. psgml mode allows for validation against the DTD. Let's validate it using C-c C-vto make sure it's okay.

Type: C-c C-v

psgml mode inserts the default validate command in the minibuffer; press Enterto run it.

Press Enterand type yto save the buffer when prompted

The *compilation*buffer indicates (somewhat cryptically) that the document is valid.

Of course, typical documents are far more complex than this one. Options on the View menu provide selective hiding and showing of elements, including an option to hide all tags, allowing you to focus on the content of the file instead.

psgml mode also offers numerous options. If you are running TEI Emacs, you'll find the File Options and User Options submenus on the XML/SGML menu. If you've installed psgml mode standalone, you'll find them on the SGML menu. Table 8-8summarizes some of the psgml commands.

Table 8-8. Bindings in psgml mode