Though not required, it is good practice to define your anchors at the beginning of your code (plugin). This makes sure that all anchors are registered immediately with the system on runtime. This also lets others easily see what anchors are available in your plugin without having to read through your code or crappy documentation.
The system will call define_anchor() if plugins attempt to hook into an anchor that does not already exist.
<?php define_anchor( $name ); ?>
$name
The name of your anchor. Make it meaningful, like “after_title” or “modify_title”.