There seems not to be any posting on CathInfo that gives an overview of the formatting for its own postings, including follow-ups.  So aside from Matthew, my background qualifies me plenty well enough to be the one here to take an initial whack at it.

It's based on a formatting language called BB-Code (BB for Bulletin Board: the term that prevailed in those bygone years when access was via dial-up modems).  The formatting codes are typed within syntactic constructs termed tags, which are delimited by the bracket symbols ("[" and "]")

• , and are typically used in pairs that enclose text to be specially formatted or otherwise processed, with the minor asymmetry that the closing tag is distinguished by also having a forward-slash ("/") immediately before the first letter inside its brackets.  The simple paired tags that've shown that they work as expected (by me) include:
  
  [b] and [/b]: bold-face text.
  [i] and [/i]: italic or oblique text (e.g.: book or periodical titles).
  [s] and [/s]: struck-through (i.e.: horizontally lined-through) text.
  [u] and [/u]: underlined text (please use sparingly if at all; a computer is not a typewriter--use italics instead--and this being the default formatting for links in the same browsers that are used to read CathInfo, gratuitous underlining confuses readers).
  
  This information on inferred formatting is known by its author to be incomplete, especially because it runs on the MercuryBoard software, which Matthew has customized to meet his own needs and preferences.  And also because I've omitted some, to be presented in follow-up postings (e.g.: the image tag, whose exact format I don't recall right now).  But maybe this thread will be worth pinning, regardless of incompleteness.
  
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  Note *: In general, follow-up postings in this thread (or other threads that describe the formatting syntax) may need to expect to create visible brackets ("[" and "]") by using the ASCII/ISO decimal codes (91 and 93) for those symbols, in what are called HTML entities.  Those entities have 3 parts, with no blanks allowed between them: they begin with an ampersand and an immediately following sharp-sign (called the "pound-sign"by United-Statesians), thus ("&#"), have the symbol number (expressed in decimal) in the middle, and end with a semicolon (";").

And now!  The pair of tags that motivated this thread!  They also use the equals-sign ("="):

[quote=user-name] and [/quote]:

A single all-enclosing pair is created automatically when the "QUOTE" button is clicked.

When it's desirable to respond point-by-point 

• , manually replicate these to format follow-ups. Do not respond point-by-point by editing someone else's text without inserting new pairs of quote-tags into the existing quoted text you're responding to, because readers will be unable to determine whose words are whose, and damage to reputation might result.
  
  It's probably contrary to many people's intuition, but when writing a response in a point-by-point style, it might be easiest to adopt the discipline of inserting quote-tags in reverse order, so that when the insertions are finished, the tags will end up positioned in their correct order, e.g., to respond to this (where user-name is always the person being responded to):
  
      [quote=user-name]Older wording-1. Older wording-2. Older wording-3.[/quote]
  
  Type in this (where insertions typed for responses are shown in green):
      [quote=user-name]Older wording-1.[/quote]
      New wording-1.
      [quote=user-name]Older wording-2.[/quote]
      New wording-2.
      [quote=user-name]Older wording-3.[/quote]
      New wording-3.
  
  Date & time are not automatically provided by clicking the "QUOTE" button, but empirically, they can be manually provided by enclosing them within parentheses before the "]" ending the opening quote-tag, more-or-less in this format:
  
  [quote=user-name (date time)]
  
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  Note *: Cough!  Neil O. cough!  trickster cough!)