6.4     Naming conventions
You can name things in any way you like, but we’ve used
the following conventions.
    
    - Classes   start   with   a   capital   letter,   words   are
    separated with underscores, subsequent words are
    not capitalised (eg. Image_file)
    
- Private names are prefixed with underscores (and
    are hidden by most of the user interface)
    
- Functions from the VIPS library are prefixed with
    im_
    
- Global utility functions (eg. map), public members
    (eg. Colour.colour_space) are all lower case, words
    are separated with underscores, subsequent words
    are not capitalised
    
- Constants            are            capitalised            (eg.
    Operator_type.COMPOUND_REWRAP)