BLINKER OVERLAY PAGEFRAME     Enable use of EMS pageframe for overlays
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 Purpose  : Enable use of the EMS pageframe for overlays

 Syntax   : BLINKER OVERLAY PAGEFRAME ON | OFF

 Default  : OFF

 Example  : # Use the EMS pageframe
            BLINKER OVERLAY PAGEFRAME ON

 Note: Please read this section fully before using this command.This command
 will allow the overlay manager to utilize the expanded memory pageframe for
 the overlay pool (maximum size 64kb), on machines equipped with LIM EMS (3.2
 or higher) expanded memory boards or emulators.

 Note: This command will be ignored at runtime in the absence of an EMS
 driver (or pageframe).

 To use this option there must be 64kb or more of available expanded memory,
 and the program's overlay OPSIZE must be less than 64kb. At runtime, if
 expanded memory is available and this option is enabled, the overlay manager
 will allocate 4 expanded memory pages, map them into the pageframe, and use
 the pageframe for overlay execution. The overlay OPSIZE will automatically
 be expanded to use all 64kb available in the pageframe, resulting in
 increased execution speed of overlaid code.

 WARNING: When using this command, your program MUST NOT use ANY functions
 which access expanded memory via the EMS pageframe UNLESS the pageframe
 mapping state is preserved, and you make sure no overlaid functions are
 called prior to restoring the mapping state.

 Additionally, overlaid functions will not be able to access expanded memory
 via the EMS pageframe UNLESS they take particular care to determine within
 which page(s) they are executing, otherwise they may map themselves out of
 memory. Failure to adhere to these guidelines will result in program
 failure, corruption of the program's expanded memory, or both. Also be aware
 that some TSRs, network drivers and disk caches do not save/restore the
 pageframe mapping state correctly, which may lead to program failure when
 overlays are executed in the pageframe. The use of the pageframe may be
 adjusted at runtime through the use of the BLINKER environment variable (see
 the 'Environment Variable' section in chapter 2).

 If both this command and the UMB command are used, and both the pageframe
 and a UMB are available, Blinker will use the pageframe in preference.

 If either or both of these are specified and are not available on the end
 user's system, Blinker will automatically ignore these commands and allocate
 the overlay area from conventional memory.

 Notes for CA-Clipper Summer '87:

 This command is only effective when the fixed overlay allocation method is
 selected with the command BLINKER OVERLAY FIXED. When this command is
 activated with CA-Clipper Summer'87, Blinker will disable CA-Clipper's use
 of expanded memory by automatically burning in the E0 setting to the CLIPPER
 environment variable.

 Notes for CA-Clipper 5.x:

 When this command is activated with CA-Clipper 5.x, Blinker will
 automatically burn in the BADCACHE setting to the CLIPPER environment
 variable, causing CA-Clipper 5.x to save the pageframe mapping state between
 each access to expanded memory. This will protect the overlay area in the
 pageframe from corruption.