Valid HTML entity references and numeric character references can be used in place of the corresponding Unicode character, with the following exceptions:
Entity and character references are not recognized in code blocks and code spans.
Entity and character references cannot stand in place of
special characters that define structural elements in
CommonMark. For example, although * can be used
in place of a literal * character, * cannot replace
* in emphasis delimiters, bullet list markers, or thematic
breaks.
Conforming CommonMark parsers need not store information about whether a particular character was represented in the source using a Unicode character or an entity reference.
Entity references consist of & + any of the valid
HTML5 entity names + ;. The
document https://html.spec.whatwg.org/entities.json
is used as an authoritative source for the valid entity
references and their corresponding code points.
& © Æ Ď
¾ ℋ ⅆ
∲ ≧̸
<p> & © Æ Ď
¾ ℋ ⅆ
∲ ≧̸</p>
Decimal numeric character
references
consist of &# + a string of 1–7 arabic digits + ;. A
numeric character reference is parsed as the corresponding
Unicode character. Invalid Unicode code points will be replaced by
the REPLACEMENT CHARACTER (U+FFFD). For security reasons,
the code point U+0000 will also be replaced by U+FFFD.
Hexadecimal numeric character
references consist of &# +
either X or x + a string of 1-6 hexadecimal digits + ;.
They too are parsed as the corresponding Unicode character (this
time specified with a hexadecimal numeral instead of decimal).
Here are some nonentities:
  &x; &#; &#x;
�
&#abcdef0;
&ThisIsNotDefined; &hi?;
<p>&nbsp &x; &#; &#x;
&#87654321;
&#abcdef0;
&ThisIsNotDefined; &hi?;</p>
Although HTML5 does accept some entity references
without a trailing semicolon (such as ©), these are not
recognized here, because it makes the grammar too ambiguous:
Strings that are not on the list of HTML5 named entities are not recognized as entity references either:
Entity and numeric character references are recognized in any context besides code spans or code blocks, including URLs, link titles, and fenced code block info strings:
[foo](/föö "föö")
<p><a href="/f%C3%B6%C3%B6" title="föö">foo</a></p>
[foo]
[foo]: /föö "föö"
<p><a href="/f%C3%B6%C3%B6" title="föö">foo</a></p>
Entity and numeric character references are treated as literal text in code spans and code blocks:
Entity and numeric character references cannot be used in place of symbols indicating structure in CommonMark documents.