Users can add formatting to contenteditable documents or elements using their browser’s features, such as common keyboard shortcuts for formatting (Ctrl-B for bold, Ctrl-I for italic, etc.) or by dragging and dropping images, links, or markup from the clipboard.

Additionally, developers can use JavaScript to apply formatting to the current selection (highlighted text).

document.execCommand('bold', false, null); // toggles bold formatting
document.execCommand('italic', false, null); // toggles italic formatting
document.execCommand('underline', false, null); // toggles underline