An if-else structure looks like this:
<if condition>
Some HTML...
</if>
Or like this:
<if condition>
Some HTML...
<else>
Some other HTML...
</if>
Elseifs are also allowed, as follows:
<if condition1>
HTML for condition 1...
<elseif condition2>
HTML for condition 2...
<elseif condition3>
HTML for condition 3...
</if>
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>
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