Readers interested in low-level commands:
2.2.3.1 Brief notes on fonts and point size.2.2.3 How is “line spacing” defined and changed in the setspace package?.2.2.2 Understanding \baselinestretch and \linespread.2.2.1.5 Using the \SetSinglespace command.2.2.1.3 Using the singlespace* environment.2.2.1.1 Using \doublespacing in the document preamble.2.1.1.1 Minimal parskip package example.2 Using LaTeX packages: setspace and parskip.