surround is poorly named

[Ptival]

Surrounding means to put stuff all around.

From that, I'd infer that surround a [b, c, d] means either a b c d a, or a b a c a d a, but definitely not b a c a d, where b and d are not "surrounded by as.

The standard library use words like intersperse or intercalate, which imply much better the idea of putting things "in between" other things, rather than all around.