OPL is also included in Psion Teklogix industrial handhelds such as the Workabout mx, and it also appeared in the lesser known Oregon 'Osaris' organiser, a broadly compatible EPOC32 device that uniquely used version 4 of the OS.
Designed by Colly Myers with the first iteration implemented by Richard Harrison and Martin Stamp.
And here is a GUI version for Nokia's Series 80 user interface: OPL is a structured programming language.
OPL interfaced with advanced Psion Series 3 features by means of operating system CALLs, but in the later Psion Series 5mx this was changed to a so-called OPX library, stored in the system read-only memory (ROM), termed the Z drive.
Other OPL features include those starting with a letter: g for graphical functions, m for menus, and d for dialogs.