The space is known as the descendant combinator. blockquote cite
selects any cite
element within a blockquote
element. Likewise for blockquote em
and blockquote i
.
In other words, it’s not “if a blockquote tag is embedded into a cite tag”, it’s the other way around (besides, you can’t place blockquote
s in cite
s in the first place).
As you note, commas group selector sequences into the same rule.