This is most easily explained by pointing to Reddit's **comment** (as in replies to a thread) editing functions, like italics, bold, etc. (*ital*, **bold**, etc.😁). Just basic stuff.

It's my understanding that all of TER -- 1. Forums 2. Reviews / Profiles 3. Private Messaging -- was / is custom written by TER programmers. Because of technical changes in the internet and programming, I think it's hard for them to keep up AND to avoid breaking what they have with each upgrade.  
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For YEARS, I have proposed that TER migrate to Open Source Forum Software  
http://www.designbombs.com/best-forum-software/
15 Best Forum Software to Build an Online Community in 2022 (Free & Premium)
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Most of those forums have better editing tools ("save draft"), reading (new posts, threading, etc.) and built-in private messaging systems that are better than TER PM (better searching, sorting, etc.).
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That way, the open source community continuously upgrades and bug fixes the software and TER just has to take care of members and accounts (no more programming!).  
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The Profile and Review software is much more unique. I'm not sure of any open source database that would easily match up with TER and allow for easy (or even difficult) migration of the old DB to a new DB. Maybe someone knows of an open source option that might work with Review submission and Profile updating. Same idea: less programming for TER so they can focus on membership and DB maintenance.
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I don't think that TER should even TRY to change the current editor because it might introduce more bugs than they can ever fix. (Changing the editor to allow bold, italics, etc. means changing the Profile software to properly display the new fonts, too. I predict a disaster.)

Thanks for the feedback. I was puzzled when I looked for the typical copyright symbol followed by one of the established forum builders, e.g.,  © vBulletin Solutions, which most online forums, incl. USASG, use. They used to have s/w to port existing forums built with bubble gum and bailing wire over to their platform. I could see how, given the ads here, that one of the established companies might have restriction, which is where your suggestion comes it.
 
They could indeed use open source s/w, platformed wherever they want (Cyprus?), and take it from there. However, not only did you ID a solution, you also ID'd the likely barrier to using it: porting their existing data. Years ago when forums started moving to established, purpose-designed forum s/w, there was at least one that I remember that had to inform it's users that all stored attachment (pics, etc.) were lost. Poof. Gone. That destroyed the forum since it was pic heavy by the nature of the forum's raison d'être. Imagine justifying that decision to stakeholders! But that was 10-15 years ago. Things have changed!
 
And who knows whether structure and s/w notation/documentation best practices were used throughout developing this site, particularly when new features and patches were applied. It could be spaghetti code that can't be ported w/o a truly large human effort, and that means $$, and that means we won't see vBulletin any time soon. But adding three or four editing functions? I'll bet there's a way to tap a PC's intrinsic resources, including fonts that you mentioned, to do that -- a la the dictionaries for spellcheck.

Or, if it is broke, don't break it worse. ...  
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I don't think you've been on TER long enough to have gone through some of their major updates. I call them upDATES, not upGRADES because they didn't always go very well. TER did not ask users what they wanted or didn't want and new code often conflicted with old code. ... And here we are.
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Also, you said, "I'll bet there's a way to tap a PC's intrinsic resources, including font s...". Well, TER has to work across ALL platforms from PCs to Macs to Linux to Android to iPhone to ... whatever else I'm forgetting to include. Post-update error reports (to the forums) included, "It worked for me on my Mac OS10 but when I upgraded to OS11 TER stopped working." "Stopped working on Chrome for Windows but works on Chrome on my Android phone." and on and on and on. After one major update, there were so many complaints that TER reverted to "TER Classic" while they tried to fix all the problems they created. As I recall, a lot of old posts were lost during one update and never recovered.  
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I don't think that adding new fonts that will work seamlessly across all platforms is as easy as you think. Is uni-code really uni-versal?  If TER has to patch it in, it will NOT be easy or guaranteed to work at all.
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I think TER should ask users for our input regarding our experiences with free open source forum software, which ones we like, don't like, and why. Migration will be a BIG headache but a ONE TIME headache. In the meantime, ...
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IF IT AIN'T BROKE, DON'T BREAK IT!