INT 21 - DOS 1+ - FIND FIRST MATCHING FILE USING FCB
AH = 11h
DS:DX -> unopened FCB (see AH=0Fh), may contain '?' wildcards
Return: AL = status
00h successful
[DTA] unopened FCB for first matching file
FFh no matching filename, or bad FCB
Notes:  the type of the returned FCB depends on whether the input FCB was a
normal or an extended FCB
for extended FCBs with search attribute 08h, the volume label (if any)
will be returned even if the current directory is not the root dir.
DOS 3+ also allows the '*' wildcard
the search FCB must not be modified if AH=12h will be used to continue
searching; DOS 3.3 has set the following parts of the FCB:
0Ch    BYTE    ???
0Dh    WORD    directory entry number of matching file
0Fh    WORD    cluster number of current directory
11h  4 BYTEs   ???
15h    BYTE    drive number (1=A:)
at least for DOS 3.3, the unopened FCB in the DTA is actually the drive
number followed by the file's directory entry
SeeAlso: AH=1Ah,AH=4Eh,INT 2F/AX=111Bh

See also: 2112

2111 - DOS 1+ - FIND FIRST MATCHING FILE USING FCB