# EPOC OPL Guide & Reference Glossary

## Index M

Term | Topic | Meaning | See Also
mask | Graphics and Interaction | A 2-bit colour bitmap which is used to store the shape of another bitmap. Masks are the same size as their related bitmap. A zero bit in a mask means that the related bitmap is transparent there, a one means that the other bitmap is not transparent in that pixel. | bitmap
MIME | Read This First | Multipurpose Internet Mail Extensions. A way of associating foreign (non-EPOC) files to their correct type and application. Files which are foreign to EPOC are recognised by MIME recognisers located in `System\Recogs\` under ER5. OPL applications can register themselves as being able to handle a given kind of MIME-recognised file using the ER5 OPL `MIME` keyword. This is in addition to the standard UID-based recognition of files provided by EPOC. See also OPL and MIME and OPL applications. | file extension, document, content type
module | Introducing OPL | One or more procedures for OPL to follow. Each OPL module is stored in a single program file. | program, procedure
multi-bitmap file | Advanced Topics | An EPOC picture file or MBM. MBMs can contain one or more bitmaps and their masks. |