modelValue is whether the sidebar this controls is expanded, bound two-way with v-model. The toggle keeps no state of its own — it renders the one you give it and asks for the other, which is what lets the sidebar's own header button and a second one in a navbar drive one sidebar without either being the source of truth.

side is which edge the sidebar being toggled sits on, and all it does is flip which way the icon's chevron points — a right-hand sidebar collapses to the right, so that's the direction the button has to promise. Both buttons below share one state; only the glyph differs.

size scales the button to sit alongside whatever else is in the bar — the same sm/md/lg steps Button takes, since that's what it renders. Sidebar renders the one in its header at the default md.

icon pins the glyph instead of letting it follow the state. By default it swaps between sidebarClose and sidebarOpen so it always shows which way the click will go — override it when you'd rather the control read as one steady thing, the way a hamburger does.

label is the accessible name. It defaults to "Collapse sidebar" or "Expand sidebar" depending on the current state, which is already the right thing for a sidebar toggle — set it when the panel is called something else in your app, so the button and the panel match.

disabled pins the sidebar where it is — for a layout that has to stay expanded on a wide screen, or a panel that shouldn't be dismissed mid-task.

Sidebar renders one of these in its own header, but nothing stops a second toggle elsewhere from sharing the state. Both read open, both write it, and neither one has to know the other exists.