Function us_append 

pub fn us_append<C: Cost>(x: Doc<C>, y: Doc<C>) -> Doc<C>

Concatenates two documents horizontally with spacing.

To combine more than two documents or an iterator of documents, use us_concat.

Equivalent to x & space() & y.

Example

let doc = us_append(text("hello"), text("world"));
assert_eq!(doc.to_string(), "hello world");