Finds wordbreaks in the buffer. start specifies a location to start searching backwards to the next word start; its value will be replaced with the starting position of the word that is found. end specifies a location for searching forward to the end of a word. Either of start and end may be NULL.
The reason parameter specifies more information about what the wordbreak is used for. For example, the wordbreaks used to move the caret may be different from the wordbreaks used to break lines. The possible values of reason are: