The \fill-line command
The \fill-line command aligns and justifies markup text by setting as many columns as required, in a given space.
In this snippet we use numbers to (beautifully) show how the command works; but when using text beware to use quotes if you want your words to stay together. For example, this code
\fill-line { The quick brown fox }
results in something like the following (i.e., four columns).
The quick brown fox
With quotes, input like
\fill-line { "The quick brown fox" }
produces output like this (i.e., a single, centered column).
The quick brown fox