This is a GDI language produced by Monotype Imaging, Inc. Used for some Lexmark (X500) and Dell (MFP 1125) printers.

$ gipddecode -h </home/rick/c500n/x500web.prn
     0: OFST    0       len=128
    80: OFST    1       len=128
   100: OFST    2       len=128
   180: OFST    3       len=128
   200: OFST    4       len=128
        [SNIP]
 27d80: OFST    1275    len=128
 27e00: \033%-12345X@PJL SET DISPINFOWHILEPRINT=OFF
 27e2a: @PJL SET DISPATPAPERCHANG=OFF
 27e49: @PJL SET JAMRECOVERY=ON
 27e62: @PJL SET OUTPUTBLANKPAPER=OFF
 27e81: @PJL SET PRINTSLOWLY=OFF
 27e9b: @PJL SET REVERSEPRINT=OFF
 27ebf: GDIJ    len=108
        unk0=0, unk1=0, unk2=0, unk3=0, unk4=0
        unk5=16777221(0x1000005), unk6=0, unk7=0, unk8=0, paper=0
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
 27f37: GDIP    len=52
        unk5 = 0x4000000, w254 = 4896, h254 = 6110
        320870622, 0, 0, 0, 0, 67108864, 0, 0, 0, 0, 0, 0, 0, 
 27f77: GDIB     0      len=3160 (0xc58)
 28be7: GDIB     1      len=17496 (0x4458)
 2d057: GDIB     2      len=11256 (0x2bf8)
 2fc67: GDIB     3      len=19128 (0x4ab8)
 34737: GDIB     4      len=59288 (0xe798)
 42ee7: GDIB     5      len=53112 (0xcf78)
 4fe77: GDIB     6      len=7192 (0x1c18)
 51aa7: GDIB     7      len=8248 (0x2038)
 53af7: GDIB     8      len=3832 (0xef8)
 54a07: GDIB     9      len=4888 (0x1318)
 55d37: GDIB    10      len=3768 (0xeb8)
 56c07: GDIB    11      len=3256 (0xcb8)
 578d7: GDIB    12      len=2680 (0xa78)
 58367: GDIB    13      len=3832 (0xef8)
 59277: GDIB    14      len=2072 (0x818)
 59aa7: GDIB    15      len=2648 (0xa58)
 5a517: GDIB    16      len=3256 (0xcb8)
 5b1e7: GDIB    17      len=3672 (0xe58)
 5c057: GDIB    18      len=216 (0xd8)
 5c147: GDIB    19      len=1240 (0x4d8)
 5c637: GDIB    20      len=2360 (0x938)
 5cf87: GDIB    21      len=216 (0xd8)
 5d077: GDIB    22      len=216 (0xd8)
 5d167: GDIB    23      len=216 (0xd8)
 5d257: GDIB    24      len=888 (0x378)
 5d5e7: PIDG
 5d5f3: JIDG