Movable Type allows for designers and developers to embed variables inside of other template tags. This gives them the flexibility of having a single tag produce a variety of outputs depending upon its context or what variables are passed into it. For example, say you wanted to display a list of related entries based upon what entry the reader happen to be looking at. You wanted to do this by finding the most recent entries from categories shared by the current entry. Make sense?

Let's compare two examples. The first displays a list of entries tagged "news" or "current events."

<ul>
<mt:entries tags="News OR Current Events">
<li><a href="<mt:entrypermalink>"><mt:entrytitle></a></li>
</mt:entries>
</ul>

Now, let's tweak that template code to display a list of entries using a variable to select which tags to filter the list by:

<mt:setvarblock name="tags"><mt:entrytags glue=" OR "/></mt:setvarblock>
<ul>
<mt:entries tags="$tags">
<li><a href="<mt:entrypermalink>"><mt:entrytitle></a></li>
</mt:entries>
</ul>

In this example, the variable is denoted using the dollar sign ($) followed by the variable name. Note that the dollar sign is not needed when declaring the variable using the <mt:SetVarBlock> template tag.

Starting with Movable Type 4.0, all template tag attributes can process variables in this fashion, opening the door for far advanced and adaptive templates.