(cffi:defcenum content-t
  (:color #x1000)
  (:alpha #x2000)
  (:color-alpha #x3000))  

:color

The surface will hold color content only.

:alpha

The surface will hold alpha content only.

:color-alpha

The surface will hold color and alpha content.

The cairo:content-t enumeration is used to describe the content that a surface will contain, whether color information, alpha information (translucence vs. opacity), or both. The large values here are designed to keep cairo:content-t values distinct from cairo:format-t values so that the implementation can detect the error if users confuse the two types.