To be honest, I can't parse the sentence to make a whole lot of sense. Maybe it should just be a sentence or two more, and could also mention that it is identical to `a[b, :]`... As a start, maybe something along: When indexing a multidimensional array, the boolean index may have fewer dimensions then the array being indexed. This is equivalent to indexing with `y[b, ...]` and <short description if you can think of one>. Then the example.

I am quite sure there is somewhere another indexing documentation. Any idea how these relate (I don't see an in depth descriptoin of advanced/fancy indexing here, but I know it exists).