How to document a custom library in Arduino
Arduino uses the keyword.txt file to highlight words and to define a reference page to keywords. But the reference page must be in reference folder of IDE installation and the keyword.txt contains only a filename, not the path.


  REFERENCE_LINK This field specifies the Arduino Language Reference page to open via Right Click > Find in Reference or Help > Find in Reference when the cursor is on that keyword. Generally it does not make sense to define the REFERENCE_LINK field for 3rd party library keywords since they are not likely to be in the Arduino Language Reference.


I have a library which implements WiFiClient and WiFiServer like the Arduino WiFi library, so I can link in keywords.txt to Arduino reference like this:

WiFiClient  KEYWORD2    WiFiClient
WiFiServer  KEYWORD2    WiFiServer
WiFiUDP     KEYWORD2    WiFiUDPConstructor


The names used are names of html files in Arduino\reference\www.arduino.cc\en\Reference.