What does "prelude" mean?

[williamyeny]

Apologies for the basic question, but I searched around and I'm still confused what "prelude" means, exactly. Is there a definition somewhere I can read up on? Or an example of a prelude? Thanks!

[lahmatiy]

There is no definition, but CSS Syntax spec is using it to name a part of a rule. For instance:

at-rule
An at-rule has a name, a prelude consisting of a list of component values, and an optional block consisting of a simple {} block.

qualified rule
A qualified rule has a prelude consisting of a list of component values, and a block consisting of a simple {} block.