A collection of a set of variants for a particular icon.
An icon factory helps you to manage a collection of GtkIconSets; and a
GtkIconSet manages a set of variants for a particular icon, that is, variants
for different sizes and widget states. Icons in an icon factory are named by
a Stock ID, which a simple string identifying the icon.
Each GtkStyle has a list of
GtkIconFactorys derived from the current theme; those
icon factories are consulted first when searching for an icon. If the theme
doesn't set a particular icon, PHP-GTK 2 looks for it in a list of default
icon factories, which are maintained by
Applications with icons must add a default icon factory to their icons,
which will allow themes to override the icons for the application.