This library helps you to define help document mode for various languages. `langdoc-define-help-mode' makes a major mode for help document and a function to show a description of a symbol. It takes at least six arguments. First three arguments are to define the help document mode. * MODE-PREFIX Symbol to make a help mode name and a function name. `langdoc-define-help-mode' makes a major mode named MODE-PREFIX-mode and a function named MODE-PREFIX-describe-symbol. * DESCRIPTION Description for MODE-PREFIX-mode. * HELPBUF-NAME Buffer name for MODE-PREFIX-mode Next three arguments are to define MODE-PREFIX-describe-symbol. * POINTED-SYM-FN Function name which returns the string pointed by the cursor. This function takes no arguments. * SYMBOL List of strings which is used to complete words. * MAKE-DOCUMENT-FN Function name which takes the word as a string and returns the help string. Rest of the arguments is to make links in help buffers. * LINK-REGEXP Regexp string to make links. If nil, MODE-PREFIX-describe-symbol does not make any links in help buffers. * LINKED-STR-FN Function name which takes substrings matched in LINK-REGEXP and returns the string to be linked. * MAKE-LINK-FN Function name which takes same arguments as LINKED-STR-FN and returns a string or a cons pair (SYM . FUN). SYM is a link to other document and FUN is the function to jump to the help buffer for SYM. If it returns a string, MODE-PREFIX-describe-symbol is used to jump to SYM. * PREFIX-STR, SUFFIX-STR Prefix and suffix of the string returned from LINKED-STR-FN. If you need a concrete example, see brainfuck-mode.el (https://github.com/tom-tan/brainfuck-mode/).