The main benefit of the TR file format was the file compression. For example - Anna Kerenina (Tolstoy) is 1936k as a txt file, and compresses to 955kb in TR2, and 846kb in TR3. For comparison the BEST compression in WinRar creates an archive of 414kb. But for a file format that retains readability, it is quite impressive.
These are the main tags used:-
<new> Indicates a new chapter (and an entry in the file index)
<a> Used to create hyperlinks within a TR file
<b>Bold text</b>
<i>Italicise text</i>
<u>Underline Text</u>
<hr> Insert Horizontal line
<br> Insert line break.
<p> The Paragraph Tag - Indicates a new paragraph of text.
<centre>Centre Text</centre> (Centre on the page)
It was based on a small subset of HTML, and is also very similar to the forum mark-up tags.
There are a few other tags, used for tables and TAB delimited (Database) type files, but the above probably represents 95% of the tags commonly used.
I have the full file spec in a MS Word Doc - culled from the help files within TR v2 and V3.
I can email it to anyone who is interested.
I have about 400 out-of-copyright TR files formatted, including about 10 different Bible versions.