Prepopulate

Prepopulate is an attempt to solve the problem that resulted from
the discussion at http://www.drupal.org/node/27155 where the $node object,
it was (correctly, I believe) decided, should
not be prefilled from the $_GET variables, and instead, the power of the
FormsAPI should be used to modify the #default_value of the form
elements themselves.

This functionality will make things like bookmarklets easier to write,
since it basically allows forms to be prefilled from the URL, using a
syntax like:

Please report any bugs or feature requests to the Prepopulate issue queue.

Instructions for use

Simple Usage

Prepopulate the title field on a node creation form:
http://www.example.com/node/add/content?edit[title]=This is the title
With 'non-clean' urls:
http://www.example.com?q=node/add/content&edit[title]=This is the title

Multiple fields

Prepopulate can handle pre-filling multiple fields from one URL. Just
separate the edit variables with an ampersand:

http://www.example.com/node/add/content?edit[title]=The title&edit[body_filter][body]=The body

You're already using the ampersand with non-clean URLs:

http://www.example.com?q=node/add/content&edit[title]=The title&edit[body_filter][body]=The body

How to find what variable to set

This can be tricky, but there are a few things to keep in mind that
should help.

Prepopulate.module is quite simple. It looks through the form, looking
for a variable that matches the name given on the URL, and puts the
value in when it finds a match. Drupal keeps HTML form entities in an
edit[] array structure. All your variables will be contained within the
edit[] array.

A good starting point is to look at the HTML code of a rendered Drupal
form. Once you find the appropriate <input /> (or <textarea>...</textarea>
tag, use the value of the name attribute in your URL, contained in the
edit array. For example, if the <input /> tag looks like this:

then try this URL:

http://www.example.com/node/add/content?edit[title]=Automatic filled in title

CCK

CCK fields are a bit more complicated:

The key is to put this in the edit[] array nested, like this:

http://www.example.com/node/add/content?edit[field_office][0][node_name]=AL-235

Another example:

would be:

http://www.example.com/node/add/content?edit[field_content][0][value]=A long text string

and, again, for non-clean URLs, it's:

http://www.example.com?q=node/add/content&edit[field_content][0][value]=A long text string

Special cases

Body fields

Body fields are different. Though their HTML entity looks like this:

You can't just take the name "body," throw it into a edit[body] and
expect it to work. Drupal wraps the body field into a "body_filter"
array when it gets processed. So, for body fields, a URL like:

http://www.example.com/node/add/content?edit[body_filter][body]=This is the body

ought to do the trick.

Escaping special characters

Some characters can't be put into URLs. Spaces, for example, work
mostly, but occasionally they'll have to be replaced with the string %20.
This is known as "percent encoding." Wikipedia has a partial list of
percent codes at:
http://en.wikipedia.org/wiki/Percent-encoding

If you're having trouble getting content into field names, or are
getting 'page not found' errors from Drupal, you should check to ensure
that illegal characters are properly encoded.