Parameters are used in many places in Joomla!:

• Item parameters
• Menu paramters
• Module parameters
• Configuration parameters (new in 1.5)

All parameters have the following attributes:

• name - This is the field name of the parameter
• type - This is the element type for the parameter, text, a list box, etc
• label - The text label to be displayed in the parameter form
• description - The text that will display when you hover over the label
• default - The default value to use

Parameters definitions are made up of one params tag and one or more param tags, for example:

<params>
  <param ... />
  <param ... />
</params>

The params tag can take the optional addpath attribute which is equivalent to calling $params?addElementPath() in the code. It should hold a full path relative to the site installation folder, for example:

<params addpath="/components/com_contact/elements">
  <param ... />

This allows any developer to define custom controls.

Selecting an Article category:

<param name="catid" type="category" default="0" label="Category" description="An article category" />

Using the section (previously scope which is also still supported) attribute, you can select categories for other components:

<param name="catid" type="category" section="com_weblinks" default="0" label="Category" description="A weblinks category" />

Selecting one of the installed wysiwyg editors:

<param name="editor" type="editors" default="" label="User Editor" description="WYSYWYG Editor for this User" />

<param name="file_name" type="imagelist" directory="/images/stories" filter="" hide_default="1" default="" label="Menu Image" description="PARAMMENUIMAGE" />

• directory - the directory in which to list the files
• filter - a regular expression to filter on, eg: filter=?\.html$? lists all files ending with .html
• exclude - a regular expression to exclude files from the list, eg: exclude=?index\.html? will exclude the index.html file from the list, exclude=?^_? will emulate private files if you name them with an underscore prefix (eg: _my_private_template.html)
• stripext - set to 1 to strip the file extension in the list
• hide_none - set to 1 to hide the ?Do not use? list option
• hide_default - set to 1 to hide the ?Use Default? list option

<param name="helpsite" type="helpsites" default="" label="Help Site" description="Help site for this User" />

<param name="menu_image" type="imagelist" directory="/images/stories" hide_default="1" default="" label="Menu Image" description="PARAMMENUIMAGE" />

• hide_default - set to 1 to hide an automatic Use Default entry in the list

<param name="language" type="languages" client="site" default="" label="Front-end Language" description="paramLanguage" />

<param name="link_titles" type="list" default="" label="Linked Titles" description="Make the Item titles linkable">
	<option value="">Use Global</option>
	<option value="0">No</option>
	<option value="1">Yes</option>
</param>

<param name="menu_item" type="menuitem" label="Menu Item" />

<param name="cache" type="radio" default="0" label="Enable Cache" description="PARAMENABLECACHE">
	<option value="0">No</option>
	<option value="1">Yes</option>
</param>

<param name="sectionid" type="section" default="0" label="Edit posts" description="Set the section to retrieve posts from" />

<param name="@spacer" type="spacer" default="" label="" description="" />

<param name="moduleclass_sfx" type="text" default="" label="Module Class Suffix" description="PARAMMODULECLASSSUFFIX" />

<param name="description_text" type="textarea" default="" label="Description Text" rows="5" cols="30" description="PARAMDESCTEXT"/>

• rows - the number of rows for the textarea
• cols - the number of columns for the textarea