Input file is amixer.1

Output from "mandoc -T lint  amixer.1": (shortened list)

      1 input text line longer than 80 bytes: This document is by ...
      4 whitespace at end of input line

Remove trailing space with: sed -e 's/  *$//'

-.-.

Output from "test-groff -mandoc -t -ww -z amixer.1": (shortened list)

      4 trailing space in the line

Remove trailing space with: sed -e 's/  *$//'

-.-.

Remove space characters (whitespace) at the end of lines.
Use "git apply ... --whitespace=fix" to fix extra space issues, or use
global configuration "core.whitespace".

Number of lines affected is

4

-.-.

Wrong distance between sentences in the input file.

  Separate the sentences and subordinate clauses; each begins on a new
line.  See man-pages(7) ("Conventions for source file layout") and
"info groff" ("Input Conventions").

  The best procedure is to always start a new sentence on a new line,
at least, if you are typing on a computer.

Remember coding: Only one command ("sentence") on each (logical) line.

E-mail: Easier to quote exactly the relevant lines.

Generally: Easier to edit the sentence.

Patches: Less unaffected text.

Search for two adjacent words is easier, when they belong to the same line,
and the same phrase.

  The amount of space between sentences in the output can then be
controlled with the ".ss" request.

Mark a final abbreviation point as such by suffixing it with "\&".

Some sentences (etc.) do not begin on a new line.

Split (sometimes) lines after a punctuation mark; before a conjunction.

  Lines with only one (or two) space(s) between sentences could be split,
so latter sentences begin on a new line.

Use

#!/usr/bin/sh

sed -e '/^\./n' \
-e 's/\([[:alpha:]]\)\.  */\1.\n/g' $1

to split lines after a sentence period.
Check result with the difference between the formatted outputs.
See also the attachment "general.bugs"

12:for the default soundcard and device. This is a good way to see a list
35:Sets the simple mixer control contents. The parameter can be the volume
54:A simple mixer control must be specified. Only one device can be controlled
61:A simple mixer control must be specified. Only one device can be controlled
74:Sets the card control contents. The identifier has these components: iface,
75:name, index, device, subdevice, numid. The next argument specifies the value
80:Shows the card control contents. The identifier has same syntax as for
98:Select the card number to control. The device name created from this
104:Select the device name to control. The default control name is 'default'.
112:Only sset and cset are accepted.  Other commands are ignored.
121:Quiet mode. Do not show results of changes.
143:will set the master volume of the second card to \-20dB.  If the master
148:will increase the PCM volume of the second card with 2dB.  When both

-.-.

Split lines longer than 80 characters into two or more lines.
Appropriate break points are the end of a sentence and a subordinate
clause; after punctuation marks.
Add "\:" to split the string for the output, "\<newline>" in the source.  

Line 169, length 91

This document is by Paul Winkler <zarmzarm@erols.com> and Jaroslav Kysela <perex@perex.cz>.

-.-.

The name of a man page is typeset in bold and the section in roman
(see man-pages(7)).

161:alsamixer(1)

-.-.

Use the name of units in text; use symbols in tables and
calculations.
The rule is to have a (no-break, \~) space between a number and
its units (see "www.bipm.org/en/publications/si-brochure")

37:a dB gain with \fIdB\fP suffix (like \-12.5dB), or an exact hardware value.
148:will increase the PCM volume of the second card with 2dB.  When both

-.-.

Put a parenthetical sentence, phrase on a separate line,
if not part of a code.
See man-pages(7), item "semantic newline".

amixer.1:37:a dB gain with \fIdB\fP suffix (like \-12.5dB), or an exact hardware value.

-.-.

Output from "test-groff  -mandoc -t -K utf8 -rF0 -rHY=0 -rCHECKSTYLE=10 -ww -z ":

an.tmac:<stdin>:1: style: .TH missing fourth argument; consider package/project name and version (e.g., "groff 1.23.0")
troff:<stdin>:116: warning: trailing space in the line
troff:<stdin>:124: warning: trailing space in the line
troff:<stdin>:129: warning: trailing space in the line
troff:<stdin>:162: warning: trailing space in the line

-.-.

Generally:

Split (sometimes) lines after a punctuation mark; before a conjunction.