Callback tag relationships. All relationships are of the form "tagname" => CallbackClass.
There are three types of tag callbacks:
| :pair: | Paired callbacks, e.g., <c:alink></c:alink>. |
| :single: | Single-tag callbacks, e.g., <c:bullet>. |
| :replace: | Single-tag replacement callbacks, e.g., <r:xref>.</r:xref></c:bullet> |
{ :pair => { }, :single => { }, :replace => { }
<code/>and<pre/>for code samples.