Various scraps and pieces of documentation. 

1. Search options.
2. Catalog options.

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1. Search options.

Search options are the options displayed in the drop-down on the left side of
the input field.

The set of search options is not catalog-specific, but rather global.
The subset of options, and their order, is however catalog specific.
An option combines a 'value' and a 'label'.
The label is displayed to the user.  The value is used internally.

a) Globally defined search options.

By default, the following options are defined 
(see libx.xul: //menupopup[@id=libx-dropdown-menupopup])

    value="Y" label="Keyword" 
    value="t" label="Title" 
    value="jt" label="Journal Title" 
    value="at" label="Article Title" 
    value="a" label="Author" 
    value="d" label="Subject" 
    value="m" label="Genre" 
    value="i" label="ISBN/ISSN" 
    value="c" label="&libx.call.number;" 
    value="j" label="Dewey" 

Using the optional //searchoptions/searchoption element, it is possible to 
redefine the labels for existing options and to add new options.

b) Options that should be displayed for each catalog.

Each catalog lists the options that should be displayed using a 
semicolon-separated string.  This string is provided in the "options" attribute 
of a catalog (child of /edition/catalogs)
If not provided, the default options depend on the catalog.
For most catalogs, it's: "Y;t;a;d;i;c", which means 
Keyword, Title, Author, Subject, ISBN/ISSN, Call Number, in that order.

Here is a list:

"scholar":      "Y;at;jt;a"
"bookmarklet":  no default, required
"millenium":    default, "Y;t;a;d;i;c"
"horizon":      default, "Y;t;a;d;i;c"
"aleph":        default, "Y;t;a;d;i;c"
"voyager":      default, "Y;t;a;d;i;c"
"sirsi":        default, "Y;t;a;d;i;c"
"sersol":       "jt;i"
"sfx":          "jt;i"
"centralsearch": no default, required
"openurlresolver":      "jt;i"

The 'options' attribute may use any predefined or additional defined options
in the list.

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2. Catalog choices.

Catalog choices are the choices displayed in the drop-down on the right 
side of the input fields.

A LibX edition displays the catalogs defined in its config.xml file,
as defined in /edition/catalogs/*

Special catalog types include "openurlresolver", which means that an
entry is added that allows searching the OpenURLResolver.

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To Do:
http://developer.mozilla.org/en/docs/Safely_accessing_content_DOM_from_chrome