This file is indexed.

/usr/share/cups/mime/indexbraille.types is in printer-driver-indexbraille 1.2.2-1+b1.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

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################################################################################
# Index Braille MIME-types handled by the printer.
application/x-idx-doc	txt string(0,<1b44>)
application/x-idx-fw	ibe string(0,<1b74>)

################################################################################
# Other MIME-types that can be handled (non-Index-Braille). The msword type is
# taken from CUPS, but seems to be disable by default.
application/msword				doc string(0,<D0CF11E0A1B11AE1>)
# application/x-brf				brf string(0,<1b>)