<fo:inline keep-together.within-line="always">This will all be kept together on a line, even squeezed to unreadable, or the product you have selected to format your FO is garbage</fo:inline>
Now, if your product cuts this off at the end or squeezes the text to fit ... it's your decision what to use, some squeeze, some cut.
Hint: Squeezing is the right answer in the above example.