else

The else attribute sets a default value for the tag to output if the field has no content.

<perch:content id="img" type="image" label="Image" else="default.png">

The equivalent to the above using perch:if tags:

<perch:if exists="img">
    <img src="<perch:content id="img" type="image">" alt="">
<perch:else>
    <img src="default.png" alt="">
</perch:if>