A sheet materialised into the project from a shipped component library. The sheet is named L_ so that it cannot clash with a user sheet, and that name is what the user sees on the canvas and in the waveform simulator; the library and component names are kept here so the catalogue can show the real name and the origin stays recoverable. Library sheets are hidden from the Sheets menu, and are reached only by asking to view one from an instance's right-click menu - which opens it read-only, and only until the project is closed (Model.OpenedLibrarySheets). They are otherwise ordinary sheets: parameter analysis, width inference and simulation all see them.