Fixes:
$ mandoc -T lint src/xfile.1
mandoc: src/xfile.1:19:1: WARNING: invalid escape sequence: \fb
$ nroff -z -man src/xfile.1
troff:src/xfile.1:19: warning: cannot select font 'b'

Fixes:
$ nroff -z -rCHECKSTYLE=1 -man src/xfile.1
an.tmac:src/xfile.1:1: style: .TH missing third argument; suggest document modification date in ISO 8601 format (YYYY-MM-DD)
an.tmac:src/xfile.1:1: style: .TH missing fourth argument; suggest package/project name and version (e.g., "groff 1.23.0")
$ mandoc -T lint src/xfile.1
mandoc: src/xfile.1:1:2: WARNING: missing date, using "": TH

groff_man_style(7):
       .TH topic section [footer‐middle] [footer‐inside] [header‐middle]
              Determine the contents of the page header and footer.
              roff systems refer to these collectively as “titles”.  The
              subject of the man page is topic and the section of the
              manual to which it belongs is section.  This use of
              “section” has nothing to do with the section headings
              otherwise discussed in this page; it arises from the
              organizational scheme of printed and bound Unix manuals.
              See man(1) or intro(1) for the manual sectioning
              applicable to your system.  topic and section are
              positioned together at the left and right in the header
              (with section in parentheses immediately appended to
              topic).  footer‐middle is centered in the footer.  The
              arrangement of the rest of the footer depends on whether
              double‐sided layout is enabled with the option -rD1.  When
              disabled (the default), footer‐inside is positioned at the
              bottom left.  Otherwise, footer‐inside appears at the
              bottom left on recto (odd‐numbered) pages, and at the
              bottom right on verso (even‐numbered) pages.  The outside
              footer is the page number, except in the continuous‐
              rendering mode enabled by the option -rcR=1, in which case
              it is the topic and section, as in the header.  header‐
              middle is centered in the header.  If section is an
              integer between 1 and 9 (inclusive), there is no need to
              specify header‐middle; an.tmac will supply text for it.
              The macro package may also abbreviate topic and footer‐
              inside with ellipses (...) if they would overrun the space
              available in the header and footer, respectively.  For
              HTML output, headers and footers are suppressed.

              Additionally, this macro breaks the page, resetting the
              number to 1 (unless the -rC1 option is given).  This
              feature is intended only for formatting multiple man
              documents in sequence.

              A valid man document calls .TH once, early in the file,
              prior to any other macro calls.

              By convention, footer‐middle is the date of the most
              recent modification to the man page source document, and
              footer‐inside is the name and version or release of the
              project providing it.

Fixes:
$ mandoc -T lint src/xfile.1
mandoc: src/xfile.1:13:45: STYLE: whitespace at end of input line
mandoc: src/xfile.1:29:28: STYLE: whitespace at end of input line
mandoc: src/xfile.1:363:62: STYLE: whitespace at end of input line

Fixes:
$ nroff -z -rCHECKSTYLE=3 -man src/xfile.1
an.tmac:src/xfile.1:30: style: blank line in input
an.tmac:src/xfile.1:349: style: blank line in input
an.tmac:src/xfile.1:352: style: blank line in input
an.tmac:src/xfile.1:355: style: blank line in input

Replace blank lines separating paragraphs with `PP` calls.

Drop blank line that ends up preceding a (sub)section heading.

groff_man_style(7) briefly offers this advice:
         Do not put blank (empty) lines in a man page source document.

The reason is that a blank line puts 1 vee of vertical space in the
document, whereas the inter-paragraph spacing amount is configurable,
and has defaulted to 0.4 vees on typesetters since the man(7) package
debuted in Seventh Edition Unix in 1979.

https://minnie.tuhs.org/cgi-bin/utree.pl?file=V7/usr/lib/tmac/tmac.an

(See the `PD` macro definition--the line starting `.de PD`.)

Fixes:
$ mandoc -T lint src/xfile.1
mandoc: src/xfile.1:23:87: STYLE: input text line longer than 80 bytes: Specify sort order: ...
mandoc: src/xfile.1:33:81: STYLE: input text line longer than 80 bytes: with the iconSize re...
mandoc: src/xfile.1:297:81: STYLE: input text line longer than 80 bytes: Specifies the file n...

I took the liberty of siting the breaks in "gui.man" such that the
formatter would produce correct inter-sentence spacing.

groff_man_style(7):
   Fundamental concepts
       groff is a programming system for typesetting: we thus often use
       the verb “to set” in the sense “to typeset”.  The formatter
       troff(1) collects words from the input and fills output lines
       with as many as will fit.  Words are separated by spaces and
       newlines.  A transition to a new output line is called a break.
       When formatted, a word may be broken at hyphens, at \% or \:
       escape sequences (see subsection “Portability” below), or at
       predetermined locations if automatic hyphenation is enabled (see
       the -rHY option in section “Options” below).  An output line may
       be supplemented with inter‐sentence space, and then optionally
       adjusted with more space to a consistent line length (see the
       -dAD option).  roff(7) details these processes.

"Unix for Beginners", Brian Kernighan, 1974:
  Hints for Preparing Documents
    Most documents go through several versions (always more than you
    expected) before they are finally finished.  Accordingly, you should
    do whatever possible to make the job of changing them easy.  First,
    when you do the purely mechanical operations of typing, type so
    subsequent editing will be easy.

    Start each sentence on a new line.  Make lines short, and break
    lines at natural places, such as after commas and semicolons, rather
    than randomly.  Since most people change documents by rewriting
    phrases and adding, deleting and rearranging sentences, these
    precautions simplify any editing you have to do later.

https://wolfram.schneider.org/bsd/7thEdManVol2/beginners/beginners.pdf

groff(7):
       ... roff documents should not
       use the \\ or \. character sequences outside of copy mode; they
       serve only to obfuscate the input.