difference between 3aafter and 3a 3aafter

1Pseudo-elements were denoted with a single colon in CSS2,
2but have been changed in CSS3
3"in order to establish a discrimination between
4pseudo-classes and pseudo-elements".
5For compatibility reasons a single colon is still allowed for the
6pseudo-elements defined in CSS 1 and CSS2.
7
8CSS2
9The ':before' and ':after' pseudo-elements can be used to
10insert generated content before or after an element's content.
11
12CSS3
13Pseudo-elements
14
15A pseudo-element is made of two colons (::) followed by
16the name of the pseudo-element.
17
18This :: notation is introduced by the current document in order
19to establish a discrimination between pseudo-classes and pseudo-elements.
20For compatibility with existing style sheets, user agents must also
21accept the previous one-colon notation for pseudo-elements introduced in
22CSS levels 1 and 2 (namely, :first-line, :first-letter, :before and :after).
23This compatibility is not allowed for the new pseudo-elements introduced in
24this specification.