This is true, but /media didn't arrive until 10.2; maybe we need to mention both?

Please run igor to check for title capitalization and other errors.

-media must have <literal> tags.

However, having this note before any text is confusing. The reader does not know why they are being told about this.

Try to write to avoid if/then sentences with a pause (comma) in the middle:

<acronym>USB</acronym> devices can be automatically mounted by
uncommenting this line in <filename>/etc/auto_master</filename>:</para>

I don't understand why the previous section says to uncomment lines in devd.conf, but this one says to add them.

I don't understand what the comment means. What does "discard" mean in this context? Is the cache for device names or filesystem buffers or something else? This is useful for -media--why? How? Look at it from the reader's point of view.

Use &man entity markup on autofs and devd.

Better to make this imperative, and again, try to rearrange to avoid if/then sentences with a pause:

Reload the configuration if &man.autofs.5; and &man.devd.8; are already running:

This is another if/then sentence with a pause.

&man.autofs.5; and &man.devd.8; can be enabled at boot time by adding
these lines to <filename>/etc/rc.conf</filename>:

devd is already running by default. Shouldn't that be service devd restart?

Passive -> active: s/will appear/appears/
Other changes to split long, confusing sentences:

<para>Each file system that can be automatically mounted appears as a directory
in <filename>/media/</filename>.  The directory is named after the file system label.
If the label is missing, the directory is named after the device node.</para>

<para>The file system is transparently mounted on the first access, and unmounted
after a period of inactivity.  Automounted drives can also be unmounted manually:

Avoid emdashes.

This mechanism is typically used for memory cards and <acronym>USB</acronym>
memory sticks.  It can be used with any block device, including optical drives or <acronym>iSCSI</acronym>
<acronym>LUN</acronym>.</para>

Unnecessary whitespace.

Hm. Perhaps "removable handling support in autofs is supported starting with 10.2-RELEASE"?

Well, it's a bit complicated. I'm not sure if we want to explain it here in length; it's just that piece of configuration file needs to be moved up, outside the comments section. The comment is just what's there at this point.

Something like that sounds good, but you want to rearrange, perhaps autofs supports automatic mounting of removable media as of FreeBSD 10.2-RELEASE

Maybe mention instead that the default config file contains a commented example of this config?

Please add a blank line before the <screen> element.

This sentence needs an article. I also suggest not numbering steps because they often become outdated.
s/Second/The next/

Please add a blank line before the <screen> element.

Please add a blank line before the <screen> element.

devd does not have the reload keyword:

# service devd reload
/etc/rc.d/devd: unknown directive 'reload'.
Usage: /etc/rc.d/devd [fast|force|one|quiet](start|stop|restart|rcvar|enabled|status|poll)

"enabled at boot time" is a little ambiguous here. "set to start at boot" is somewhat clearer.

devd is enabled by default. Maybe remove that line and note that devd is required?

<para>&man.autofs.5; can be set to start at boot by adding this line to
<filename>/etc/rc.conf</filename>:</para>

<programlisting>autofs_enable="YES"</programlisting>

<para>&man.autofs.5; requires &man.devd.8; to be enabled, as it is by default.</para>

Only one blank line between elements.

Or just Then add the following lines...?
Or Move the following lines out of the commented section?

I think if we mention that it relies on devd we should also include that it's enabled by default -- otherwise I can imagine a new user looking for the missing instructions to enable devd.

Then add or uncomment these lines in <filename>/etc/devd.conf</filename>:

This also avoids the semicolon.

Um... isn't that what the last part of that sentence does?

<para>&man.autofs.5; requires &man.devd.8; to be enabled, as it is by default.</para>

I don't think "uncomment" works well in this situation, where there aren't single lines to uncomment.

Here it's

/*

... a huge amount of unrelated stuff ...

​notify 100 {
	​        match "system" "GEOM";
	​        match "subsystem" "DEV";
	​        action "/usr/sbin/automount -c";
	​};

... a huge amount of additional unrelated stuff ...

*/

To me "uncomment" implies that the user can either remove a few # characters, or delete /* and */ perhaps, not obtain a set of lines out of the middle of a large block.

I see what you mean. In other places, we generally ignore what might already be present in files. I'd suggest that here, also. Just show the lines to add, and ignore whatever might be present already in comments. The document can't count on the comment being there. Neither can the comment count on what might be documented. "Don't repeat yourself" should be applied here. It is too easy for multiple copies of things to get out of sync, and I'd say the comment should be removed.

Needs a blank line before the new section.

"The" is not needed.

"the following" is almost always redundant.
s/the following/these/

Please split the sentences instead of splicing them with a semicolon. The second sentence needs an article ("The default").

However, I repeat: it is a mistake to state what the default configuration file contains, because that file can change without the documentation being updated. Better to tell the user what is needed and ignore whatever might or might not be in the example config file. So that whole sentence becomes just:

Then add these lines to <filename>/etc/devd.conf</filename>:</para>