These should all get escaped:
Backslash: \\
Backtick: \`
Asterisk: \*
Underscore: \_
Left brace: \{
Right brace: \}
Left bracket: \[
Right bracket: \]
Left paren: \(
Right paren: \)
Greater-than: \>
Hash: \#
Period: \.
Bang: \!
Plus: \+
Minus: \-
These should not, because they occur within a code block:
Backslash: \\
Backtick: \`
Asterisk: \*
Underscore: \_
Left brace: \{
Right brace: \}
Left bracket: \[
Right bracket: \]
Left paren: \(
Right paren: \)
Greater-than: \>
Hash: \#
Period: \.
Bang: \!
Plus: \+
Minus: \-
Nor should these, which occur in code spans:
Backslash: `\\`
Backtick: `` \` ``
Asterisk: `\*`
Underscore: `\_`
Left brace: `\{`
Right brace: `\}`
Left bracket: `\[`
Right bracket: `\]`
Left paren: `\(`
Right paren: `\)`
Greater-than: `\>`
Hash: `\#`
Period: `\.`
Bang: `\!`
Plus: `\+`
Minus: `\-`