$[deferred_content refs] - Deferred Content References

These are identical to ${content_refs}, but are evaluated only after all other references.

$[name]

This means that a content variable can be set at the end of an <out> section, but referred to at the start, for example. Handy for HTML page titles.

In addition, this is the recommended way to access metadata set using the wmmeta tag.

Again, a default value can be supplied, using this format:

$[name?defaultvalue]