Character Notation Render
a1 word space   | |
a2 no-break space   | |
en space   | |
en quad   | |
em quad   | |
em space   | |
a6 three-per-em   | |
a7 four-per-em   | |
a7 six-per-em   | |
figure space   | |
a2 Punctuation space   | |
a4 thin space   | |
a5 hair space   | |

En & Em

Two useful spaces in the HTML repertoire are the en space   and the em space  .
Both are visibly wider than a normal space, as mandated in the official HTML specification.

Character Code Render
zero width space ​ |​|
zero width non-joiner ‌ |‌|
zero width joiner ‍ |‍|
zero width no-break space  ||
left-to-right mark ‎ |‎|
right-to-left mark ‏ |‏|
line separator 
 |
|
paragraph separator 
 |
|
left-to-right embedding ‪ |‪|
right-to-left embedding ‫ |‫|
formatting ‬ |‬|
left-to-right override ‭ |‭|
right-to-left override ‮ |‮|
left-to-right mark ‎ |‎|
right-to-left mark ‏ |‏|

Outer spaces

Sometimes in typesetting you need to provide a hint that the computer can break a long word in a particular position without any other interpretation or visible indication.
This is the zero width space : ​
Its twin is the zero width no-break space :  which can be used to keep a word from breaking at that point.

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