It isn't clear to me if code such as the following is unique to Outlook only:
<p><!--[if mso]><br><![endif]--></p>
Looking up info re "mso" I find that it means "MS Office", however all the examples on the web refer to Outlook being the target for this conditional html code.
Q: Does MS Word or OneNote also generate conditional html as above? Or is it unique to MS Outlook?
Update (again): I tried copying from MS Word and Outlook programs and it does make use of the conditional formatting, however it looks different to the conditional formatting I gave earlier. We are trying to figure out what actually generated the above example which was submitted by a student and it looks like they copied from MS Word or an email.
By copying text into Drupal I've found both MS Word and Outlook programs produce this code:
<p class="MsoNormal">1<br> 2</p>
<p> </p>
<p class="MsoNormal">3</p>
<p> </p>
<p><!-- [if gte mso 9]><xml>
<o:OfficeDocumentSettings>
<o:AllowPNG />
</o:OfficeDocumentSettings>
</xml><![endif]--><!-- [if gte mso 9]><xml>
<w:WordDocument>
<w:View>Normal</w:View>
<w:Zoom>0</w:Zoom>
<w:TrackMoves />
<w:TrackFormatting />
<w:PunctuationKerning />
... and it just keeps going with 600+ lines of Word generated code..
Meanwhile Outlook Webmail (outlook.office365.com) generated html like this:
<div style="font-family: Arial, Helvetica, sans-serif; font-size: 12pt; color: #000000;">1</div>
<div style="font-family: Arial, Helvetica, sans-serif; font-size: 12pt; color: #000000;"> </div>
<div style="font-family: Arial, Helvetica, sans-serif; font-size: 12pt; color: #000000;">2</div>
<div style="font-family: Arial, Helvetica, sans-serif; font-size: 12pt; color: #000000;"> </div>
<div style="font-family: Arial, Helvetica, sans-serif; font-size: 12pt; color: #000000;">3<br><br>4</div>
<div style="font-family: Arial, Helvetica, sans-serif; font-size: 12pt; color: #000000;"> </div>
<div style="font-family: Arial, Helvetica, sans-serif; font-size: 12pt; color: #000000;"><br>
Source Found: We eventually found the source of the code - Matlab Online. Strange for a non MS product to produce the "mso" tags, but it clearly does when using Firefox and Chrome browsers (but not in Safari).
HTML in Outlook is rendered and edited by Word (there is a Word-light dll used by Outlook), so yes, both Outlook and Word use it.