Many of these tags have a scope argument. The valid values for the scope argument are "tag", "portlet request", "http request", "session", "persistent session", "application". NOTE: These values are not case-sensitive, but it is considered a best practice to use all lower case.

Various tags also set editable shared variables as part of their execution. If a variable with the same name already exists, it will be overwritten. If the pre-existing variable is not editable, then the tag will fail. Variable names cannot contain the reserved character '.'.

Display tags need data tags to provide them with content to display since they only contain the logic for formatting and generating HTML. The actual content is provided with data tags.

Every display tag has a mechanism to consume data tags. The most straight-forward way is via an attribute that takes an identifier (ID) that every Data Tag needs to declare.

Some of these tags have a scope argument. The valid values for the scope argument are "tag", "portlet request", "http request", "session", "persistent session", "application". These values are not case-sensitive, although it is considered a best practice to use all lower case.

The display tags in the Navigation tag library (plugnav) require PTURL DO data found in the Data Tag library (ptdata).

See the Data tag library (ptdata) for definitions of the different types of data.

Data tags provide content for display tags, which format and display the content. Data tags do not actually display anything, all they do is to set data on the tag scopes, such as the session or the portlet request scope. The data stored by these tags on the tag scopes are used by display tags. For example, the ptnavtags:ptddmenutab tag generates HTML for a DHTML dropdown menu. It does not display any content by default. To populate the menu with entries, it requires a reference to one or more data tags. The way to specify what data tag to use in a display tag is to reference the ID attribute that all data tags should define. A display tag defines an attribute to specify the data tag ID to use.

There are several types of data tags and display tags defined since not all data tags or display tags are compatible with each other. The ALI framework tag libraries (core, logic, standard, ui, data and navtags) provide three types of data tags.

Two of these types are intrinsic to the tag framework, the string data and the IDataObject (DO) data. These two types are used by the tag framework to enable text replacement operations with the $ operator.

1. The String data type is the most basic type. As the name suggests, the data consists of a text string. These strings can be read from Tag scopes by display tags. They can also be used with the $ operator prepended to the data tag ID in the HTML document or in tag attributes, for example,
   
   myattribute="$mytag"

2. The DO data type sets a container with name/value pairs on tag scopes. It is useful for collections of data, for example storing user information. A user could have a name/value pair for their name, age, address and other information. Besides being used by display tags, the name/value pairs in a DO data type are also accessible with the $ operator. Similarly to the string data type, the $ character is prepended to the data ID, and then followed by a dot and the name of any name/value in the DO data, such as:
   
   myattribute="$mytag.myname"

3. The third data type, PTURL data, is a type of DO data that only stores URLs and any information related to a URL. It contains a set of a name/value pairs, also known as URL components, such as the title of the url, the url itself, uri, the image associated with the URL and its height and width. Exactly what information the PTURL stores depends on the type of tag that generates it. As a type of DO data type, PTURL data can be used by any DO data compatible display tags. Note that display tags specifically using PTURL data do not work with non-PTURL DO data.