Customization of tree elements associated with @-commands is done with different functions than those used for other tree elements, for instance containers with a type and tree elements holding text.
There are two main functions for each element command or type, one called when the element is first encountered, and the other called after formatting the contents of the element. The actual conversion is usually done after formatting the contents of the element, but it may sometime be necessary to have some code run when the element is first encountered.
For @-commands with both a command name and a type, the type is used
as selector for the formating function for def_line,
definfoenclose_command and index_entry_command types.