A {block 'name'} pair plays one of two roles, depending on where it stands. In a layout or a directory's _inits.pad/_exits.pad it is a region: its content is the default that renders unless something overrides it. A block standing directly in a page's own template - not inside another tag - is an override: it replaces the region of that name in the page's frame, the layout it {extends} or its directories' wrappers. Inside an override, {parent} is the content it replaces, so a page can add to a region instead of replacing it.

Like {extends}, the blocks are resolved in the text while the page is assembled and are gone before it renders, so they cost nothing at render time. This lets a page without any PHP set its wrapper's title: {block 'title'}Sales{/block} replaces the {block 'title'}...{/block} in the <title> of _inits.pad. A block of a page that overrides nothing stays where it stands and renders its content.

The name must be quoted: a {block} without one (the _common snippet of that name) is not a layout block. A block that reaches the render - one in a snippet or a custom tag's template, where nothing overrides it - simply renders its content. Under the strict check, a block of an extending page that overrides no block of the layout is an error, as is a block that never closes. What stands between {ignore} tags is left alone.