Mackie C4 Commander Programming Manual page 5

<Mask> This tag denotes a single mask element
which specifies all data needed to apply a mask
on a parameter message. This is the beginning
of a single mask's definition, and each mask
definition segment needs to be terminated by a
corresponding </Mask>
<Name> The string identifier used to apply a
particular mask on a parameter message (e.g.,
<Param mask="channel">), where Name would
be "channel".
<Byte> An integer indicating which byte of
the message (one-based, from the left) is to be
masked.
<Bit> An integer indicating which bit of the
message byte (one-based, from the right) is the
left-most (starting) bit of the mask.
<Size> The number of bits this mask covers.
<Source> This value determines where the
mask data is being pulled from. If a parameter
ID is used, the value of that parameter will be
used as the mask data. The following reserved
keywords are used to indicate internal data
sources:
Data — use the current V-Pot value
Channel — use the current V-Pot channel
<SourceBit> An integer indicating which bit of
the data source (one-based, from the right) is
the left-most (starting) bit of the mask data.
C4 Commander
Programmer's Guide