Plugins are Python modules that reside in the pse/plugins
directory. Modules are loaded in lexigraphical order, so you can
control the order in which plugins load by prepending a number value
to the file name. The file name cannot start with the underscore
("_") character. You can easily temporarily disable a
module from loading at all by prepending the file name with an
In order for the module to be used by PSE, the module has to define
certain attributes and functions. These are described below.