AniJS (GitHub: anijs / anijs, License: MIT) by Dariel Noel Vila Plagado is a declarative library for CSS animations. There's a cool example that illustrates the sentence definition API, where the API calls are broken up into a form with separate fields for "if, on, do, to":
The actual markup uses data attributes to define the animation behaviour:
data-anijs="if: click, on: footer, do: swing".
The generalised format for this is explained using a simple text diagram in the wiki:
Declaration - Sentence 1; ... ; Sentence n Sentence - Definition, ... , Definition n Definition - if | on | do | to | before | after | helper