TECO has a number of internal mode flags which can be
  set and/or read to modify the standard TECO environment.

  To read the value of a flag, use
      Fx
  where "F" is the name of the flag and "x" is a command
  which accepts a numeric argument.

  To set the value of a flag, use
      xF
  where "F" is the name of a flag and "x" is a number or
  a command which returns a numeric value.

1  –  ED

  Value  Meaning if Set

      1  ^ (up-arrow) in search arguments is a literal ^

         (If 0, ^ in search arguments means that the next
         character should be interpreted as a control character)

      2  Disables Yank protection

         (If 0, the Y, N, and _ commands are aborted if they
         would result in data being lost)

      4  Disallow memory expansion when reading in a text page

         (If 0, memory is expanded, if needed, so that the whole
         text page fits in the text buffer)

      8  Unimplemented by TECO under OpenVMS...

     16  Leaves buffer pointer unchanged on search failures

         (If 0, search failures move the buffer pointer to the
         beginning of the text buffer)

     32  Enable immediate mode commands

     64  Only move the buffer pointer by one on iterative
         search failures

         (If 0, the buffer pointer moves by the length of
         the search string on iterative search failures)

    128  Disable scrolling's automatic text buffer display
         prior to TECO's prompt

         (If 0, the text buffer display is automatically
         updated just prior to TECO's prompt when scrolling
         is enabled)

  Multiple values may be combined in the ED flag

2  –  EH

  The EH flag controls TECO's action when an error is encountered.

  Value  Meaning if Set

      0  Same as 2

      1  Only the 3-character error code is printed

      2  The 3-character error code and a short message are printed

      3  The 3-character error code, a short message, and a
         more detailed explanation of the error are printed

      4  The command(s) which lead to the error are printed,
         simulating the effect of the "?" command

  The 4 may be combined with either 0, 1, 2, or 3 in the EH flag

3  –  ET

  Value  Meaning if set

      1  Type-out is in pass-all mode
      2  Terminal is a scope
      4  Terminal has lower-case; accept lower-case
      8  ^T reads with no echo
     16  Cancels ^O on output
     32  ^T reads with no wait (^T returns -1 if no input)
     64  Unimplemented by TECO under OpenVMS...
    128  TECO aborts if an error is encountered
    256  Output is truncated to the terminal's width
    512  "W" commands are supported for this scope terminal
   1024  Unimplemented by TECO under OpenVMS...
   2048  Unimplemented by TECO under OpenVMS...
   4096  Terminal is an 8-bit terminal
   8192  Accept accent grave (`) as ESCape for command input
  32768  Traps CTRL/C's (reset if CTRL/C is typed)

  Multiple values may be combined in the ET flag

4  –  EU

  Value  Meaning

      0  Flags lower case characters on output with "T"
         or "V" commands

     >0  Flags upper case characters on output

     <0  No case flagging on output

5  –  ^X

  Value  Meaning

      0  Either case matches in searches
    <>0  Exact case matches are required in searches