Editing DocBook with Vi

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Folding

As of VIM 7.0 support for folds is included in the editor. Folds allow sections of a document which are not being actively worked on to be 'folded' into themselves and hidden. Programmers often use folds to hide and show functions, classes and structures but the functionality is equally useful when editing DocBook XML.

Fold methods

Whether VIM folds content and how it folds it depends on the foldmethod setting. There are a number of valid options:

• manual - Folds are created manually.
• indent - Folds are created based on indentation levels.
• expr - Folds are created based on the value of foldexpr.
• marker - Folds are created based on markers.
• syntax - Folds are created based on syntax highlighting items.
• diff - Folds are created based on whether text has/hasn't changed, text that hasn't changed is folded.

When working with consistently indented XML content for example the indent method is very easy to invoke and requires no additional setup. It can be accessed by issuing:

set foldmethod=indent

Issuing this command while a consistently indented XML file is open in the buffer will result in a number of folds being created. Folds can be opened by placing the cursor on the line denoting the fold. For example in the following XML block there is an appendix opened on line 4 and closed on line 184. The enclosed content is a fold which contains 179 lines of text.

  4 <appendix id="chap-RedHat_Enterprise_Virtualization-Administration_Guide-Backup_and_Recovery">
  5 +--179 lines: <title>&PRODUCT; Manager backup and recovery</title>----------------
184 </appendix>     

Information on the various fold methods and how they handle folds can be accessed by issuing :help foldmethod in VIM.

Work with folds

Some frequently used commands when working with folds are:

• Use zo to open the fold under the cursor.
• Use zc to close the fold under the cursor.
• Use zR to open all folds in the buffer.
• Use zM to close all folds in the buffer.
• Use zf to create a fold from a visual selection when foldmethod is set to manual.
• Use zd to delete a fold at the cursor when foldmethod is set to manual.

There are many other options to facilitate modification of the way folds behave in VIM. Further information on the use of folds in VIM can be accessed by issuing :help fold from command mode.

Save folds across sessions

By default folds are discarded when exiting. Folds can be explicitly written to disk by issuing :mkview. When the file is next opened :loadview can be issued to reload previously saved folds for the document. Alternatively the following lines can be placed in the users .vimrc file to ensure that folds are automatically loaded and saved when buffers are opened and closed respectively.

au BufWinLeave * mkview
au BufWinEnter * silent loadview

Vi config file hacks

Set options per file

For convenient editing, I add the following lines to the bottom of any DocBook files I'll be editing in Vi(m):

<!-- 
vim: softtabstop=2:shiftwidth=2:expandtab:textwidth=72 
-->

Block indentation

To support quick indentation of visually selected blocks keys can be bound to decrease and increase the indentation level. In the example .vimrc lines below the '<' key is bound to decrease indentation and the '>' key is bound to increase indentation.

vnoremap < <gv
vnoremap > >gv