Conditional Blocks

An if-else structure looks like this:

<if condition>
    Some HTML...
</if>
	

Or like this:

<if condition>
    Some HTML...
<else>
    Some other HTML...
</if>
	

Or like this:

<if condition>
    Some HTML...
<elseif condition2>
    Some other HTML...
<else>
     Yet some more HTML....
</if>
	

Note that you can have an arbitrary number of "elseif" blocks.

The condition should be a boolean expression. For example:

<if !(color == "blue" || color == "violet")>
    You have an unusual favorite color.
</if>

<if foo && (!(bar || baz) || elephant)>
    Tweedledee.
</if>
	

Since undefined, null, and empty values evaluate to false, it is convenient to use idioms like the following:

<if error>
    <p>Your request cannot be processed because of the following error:<br>
    ${error}
<else>
    (display results...)
</if>
	

Since undefined, null, and empty values are considered equal, the following two statements are equivalent, whether foo is defined or not:

<if foo> ... </if>

<if foo != ""> ... </if>