Hi all,

I'm going to write my own parser for YAML.
But now I can't understand the following production.
What does this mean?  c = block-out ⇒ s-block-line-prefix(n) and what are "block-out" and "block-in" ?
Can anyone explain this clearly to me?

[67]s-line-prefix(n,c) ::=c = block-out ⇒ s-block-line-prefix(n)
c = block-in  ⇒ s-block-line-prefix(n)
c = flow-out  ⇒ s-flow-line-prefix(n)
c = flow-in   ⇒ s-flow-line-prefix(n)

Thanks.
Jinjun