prince-wrap-inside: auto | phrase | avoid
prince-wrap-inside:phrase is for marking up a phrase that one would weakly prefer to keep on a single line.
It adds to Prince's perceived cost of breaking within that phrase, but only a small cost, comparable to the cost of hyphenating a compound adjective such as ‘midyear’.
prince-wrap-inside:avoid is a stronger directive: it avoids breaking the text to which the property is applied even if it causes the affected text to be unusually tight, or the previous line to be unusually loose; but not if either line would become truly exceptionally tightly or loosely spaced.
(Limitation: At the time of writing, prince-wrap-inside only affects justified text.)
This property only applies to Prince for Books.