ChangeLog (brief summary of your edit for later reference):
No HTML.
A line begins with ";;" doesn't appear in the output (comment).
A line begins with "~" is treated as if it is continued from the previous line, except comments. (line continuation).
Empty line to separating paragraphs (<p>)
"- ", "-- " and "--- " ... at the beginning of a line for an item of unordered list (<ul>). Put a space after dash(es).
"# ", "## ", "### " ... at the beginning of a line for an item of ordered list (<ol>). Put a space after #'s.
A line with only "----" is <hr>.
":item:description" at the beginning of a line is <dl>. The item includes all colons but the last one. If you want to include a colon in the description, put it in the next line.
[[Name]] to make "Name" a WikiName. Note that a simple mixed-case word doesn't become a WikiName. "Name" beginning with "$" has special meanings (e.g. "[[$date]]" is replaced for the time at the editing.)
A URL-like string beginning with "http:" becomes a link. "[URL name]" becomes a name that linked to URL.
Surround words by two single quotes (''foo'') to emphasize.
Surround words by three single quotes ('''foo''') to emphasize more.
"*", "**" and "***"' ... at the beginning of a line is a header. Put a space after the asterisk(s).
Whitespace(s) at the beginning of line for preformatted text.
A line of "{{{" starts verbatim text, which ends with a line of "}}}". No formatting is done in verbatim text. Even comments and line continuation don't have effect.
A line begins with "||" and also ends with "||" becomes a row of a table. Consecutive rows forms a table. Inside a row, "||" delimits columns.
"~%" is replaced for "<br>".
If you want to use special characters at the beginning of line, put six consecutive single quotes. It emphasizes a null string, so it's effectively nothing.