Practical guide to CSS user-select, the property that controls how text can be highlighted in web UIs. Covers values (none, text, all, element) and when to use them: prevent selection on logos, allow copy on paragraphs, or pair with JS for custom behaviors like row/column or sentence selection. Notes quirks: uneven browser support, Firefox-only effects, wrapping/multiline edge cases, touch issues, and pointer-events/cursor interplay.