HTML output formatting in user-defined code should take into account the conversion context, can access converter information and use converter functions to convert Perl Texinfo trees. There are also several conventions and constraints that user defined code should abide to when formatting HTML, in order to comply with customization option values, avoid modifying structures that should not be modified, and also to have information correctly registered in the converter.
Formatting of HTML output should be used in formatting functions (see Customization and Use of Formatting Functions), tree elements conversion functions (see Tree Element Conversion Customization) and output units conversion functions (see Output Units Conversion Functions) described later on. Tree elements and output units conversion functions can also be used to output HTML, how to retrieve the corresponding function references and call those functions is also described with the functions customization.