Functions used for tree elements associated with @-commands are considered separately from functions used for tree elements not associated with @-commands, which includes containers with a type and text. There are two 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.