Character Entity References

• the keyboard does not provide a key for the character, such
  as on U.S. keyboards which do not provide European characters.

• the character may be interpreted as SGML coding, such as the ampersand (&),
  double quotes ("), the lesser than (<) and greater than(>) characters.

A character entity is represented in an HTML document as an SGML entity whose name is defined in the HTML DTD.
The HTML DTD includes a character entity for each of the SGML markup characters and for each of the printing
characters in the upper half of Latin-1, so that one may reference them by name if it is inconvenient to enter them directly:

the ampersand (&), double quotes ("), lesser than(<) and greater than(>) characters

e.g.:  Kurt Gödel was a famous logician and mathematician.

NOTES:

•   To ensure that a string of characters is not interpreted as markup,
    represent all occurrences of <, >, and & by character or entity references.
  
•   There are SGML features, CDATA and RCDATA, to allow most <, >, and & characters
    to be entered without the use of entity or character references.
•   Because these features tend to be used and implemented inconsistently,
    and because they require 8-bit characters to represent non-ASCII characters,
    they are not used in this version of the HTML DTD.
•   An earlier HTML specification included an example element whose syntax is not expressible in SGML.
    No markup was recognised inside of the Example element.
    While HTML user agents are encouraged to support this idiom, its use is deprecated.

The following entity names are used in HTML, always prefixed by ampersand (&) and followed by a semicolon(;)

The following table lists each of the characters specified in the Added Latin 1
entity set, along with its name, syntax for use, and description.
This list is derived from ISO Standard 8879:1986//ENTITIES Added Latin 1//EN.

HTML supports the entire entity set.

• reg - ® - Registered TradeMark
  
• copy - © - Copyright
  
• nbsp -   - Non-breaking space