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5.37.1 Warnings
---------------

Warning diagnostics emitted by GNU 'troff' are divided into named,
numbered categories.  The name associated with each warning category is
used by the '-w' and '-W' options.  Each category is also assigned a
power of two; the sum of enabled category values is used by the 'warn'
request and the '.warn' register.

   Warnings of each category are produced under the following
circumstances.

'char'
'1'
     No mounted font defines a glyph for the requested character.  This
     category is enabled by default.

'number'
'2'
     An invalid numeric expression was encountered.  This category is
     enabled by default.  *Note Numeric Expressions::.

'break'
'4'
     A filled output line could not be broken such that its length was
     less than the output line length '\n[.l]'.  This category is
     enabled by default.

'delim'
'8'
     The closing delimiter in an escape sequence was missing or
     mismatched.

'el'
'16'
     The 'el' request was encountered with no prior corresponding 'ie'
     request.  *Note if-else::.

'scale'
'32'
     A scaling unit inappropriate to its context was used in a numeric
     expression.

'range'
'64'
     A numeric expression was out of range for its context.

'syntax'
'128'
     A self-contradictory hyphenation mode was requested; an empty or
     incomplete numeric expression was encountered; an operand to a
     numeric operator was missing; an attempt was made to define a
     recursive, empty, or nonsensical character class; or a 'groff'
     extension conditional expression operator was used while in
     compatibility mode.

'di'
'256'
     A 'di', 'da', 'box', or 'boxa' request was invoked without an
     argument when there was no current diversion.

'mac'
'512'
     An undefined string, macro, or diversion was used.  When such an
     object is dereferenced, an empty one of that name is automatically
     created.  So, unless it is later deleted, at most one warning is
     given for each.

     This warning is also emitted upon an attempt to move an unplanted
     trap macro (*note Page Location Traps::).  In such cases, the
     unplanted macro is _not_ dereferenced, so it is not created if it
     does not exist.

'reg'
'1024'
     An undefined register was used.  When an undefined register is
     dereferenced, it is automatically defined with a value of 0.  So,
     unless it is later deleted, at most one warning is given for each.

'tab'
'2048'
     A tab character was encountered where a number was expected, or
     appeared in an unquoted macro argument.

'right-brace'
'4096'
     A right brace escape sequence '\}' was encountered where a number
     was expected.

'missing'
'8192'
     A request was invoked with a mandatory argument absent.

'input'
'16384'
     An invalid character occurred on the input stream.

'escape'
'32768'
     An unsupported escape sequence was encountered.

'space'
'65536'
     A space was missing between a request or macro and its argument.
     This warning is produced when an undefined name longer than two
     characters is encountered and the first two characters of the name
     constitute a defined name.  No request is invoked, no macro called,
     and an empty macro is not defined.  This category is enabled by
     default.  It never occurs in compatibility mode.

'font'
'131072'
     A non-existent font was selected, or the selection was ignored
     because a font selection escape sequence was used after the output
     line continuation escape sequence on an input line.  This category
     is enabled by default.

'ig'
'262144'
     An invalid escape sequence occurred in input ignored using the 'ig'
     request.  This warning category diagnoses a condition that is an
     error when it occurs in non-ignored input.

'color'
'524288'
     An undefined color was selected, an attempt was made to define a
     color using an unrecognized color space, an invalid component in a
     color definition was encountered, or an attempt was made to
     redefine a default color.

'file'
'1048576'
     An attempt was made to load a file that does not exist.  This
     category is enabled by default.

   Two warning names group other warning categories for convenience.

'all'
     All warning categories except 'di', 'mac' and 'reg'.  This
     shorthand is intended to produce all warnings that are useful with
     macro packages written for AT&T 'troff' and its descendants, which
     have less fastidious diagnostics than GNU 'troff'.

'w'
     All warning categories.  Authors of documents and macro packages
     targeting 'groff' are encouraged to use this setting.