Non separable combinations
Combinations such as “Mr. X”, “Dr. Who”, “§ 120”, “$ 120,000”, “26 %” and so on should not be separated. You wouldn’t want a $-sign at the end of the line and the amount in Dollars at the beginning of the next line. In case there is not enough space to fit both on the one line you would want them to slip pairwise to the next line. The keyboard shortcut Shift + Ctrl + Space (menu Insert › Formatting mark › Non-breaking space) between the two elements instead of a simple Space ensures both stick together.