{slot} gives a custom tag - a template in _tags/ or _common, or an _include snippet used as a pair - more than one place for the caller's content. Like {block} it plays two roles depending on where it stands.

• A {slot 'name'} pair standing directly in the content of a custom tag where it is used is a fill. It is taken out of the content when the tag opens and kept for that one use of the tag; the rest of the content goes to the template's @content@. {slot 'name'/} there is an empty fill.
• Every other {slot} - in the tag's template - is a place: the fill renders there, or, when the caller gave none, the slot's own content as a default.

A default that holds @content@ is a frame around the fill: {slot 'footer'}<footer>@content@</footer>{/slot} renders the footer element only when there is a fill to put in it; otherwise its @else@ part, or nothing. A fill is the caller's text: it renders with the caller's variables, and a {#name} or {slot} inside it belongs to the caller's own tag, which is how a template passes a slot of its own on to a tag it uses. From a tag's PHP, padSlotFill ( 'footer' ) reads a fill.

Under the strict check a slot without a name, and a slot outside any custom tag, are errors. The examples use the application's tag _tags/slotCard.pad, a card with a title slot (default Untitled) and a framed footer slot.