Access key

A menu title reading File with the F underlined is saying two things at once: what the menu is called, and which single letter reaches it. Hold the access modifier (Alt on Windows and most Linux desktops) and every mnemonic in sight is drawn; press the letter and the menu opens. Inside the menu the letters keep working on their own, so New window is Alt, then F, then N, and the pointer was never needed. The underline is the whole discovery mechanism: the letter is not something to memorise, it is something to look at.

An access key is not a keyboard shortcut, even though both are keys that run commands. A shortcut is a global binding, learned once and pressed from anywhere, and its letters have no relationship to what happens to be on screen. An access key is a navigation aid tied to a visible label. It only exists while the thing it names is showing, it is chosen out of that label’s own spelling, and it walks the interface one level at a time rather than jumping straight to an action. That is also why the two are pressed differently: a chorded shortcut is held together, a key sequence is pressed one key after another, and an access key is usually both, since the modifier arms a mode and the letters that follow are pressed alone. The demo above latches on Alt for exactly that reason, unlike a quasimode, which lasts only as long as the key is down.

Assigning the letters is fussier than it looks. Every item in one menu needs a distinct letter, the first letter is preferred and the first strong consonant is the usual fallback, and the choice travels with the translated label rather than with the command, which is why toolkits put the marker inside the string itself (&File) and let translators move it. Get it wrong and two items answer the same key, which turns a jump into a cycle.

The honest caveat is that HTML already has an accesskey attribute for this and almost nobody ships it. Browsers claim the modifier combinations for their own commands, the combination differs by browser and platform, screen readers layer their own keys on top, and there is no dependable way to tell a reader which letters are live. Most design systems therefore draw mnemonics themselves: an underline in the label, a mode armed by the modifier, and their own key handling, which is exactly what the specimen above does and why it says so on its face.