The core protocol specifies the use of server-side fonts. Such fonts are stored as files, and the server accesses them either directly via the local filesystem or via the network from another program called "font server". Clients can request the list of fonts available to the server and can request a font to be loaded (if not already) or unloaded (if not used by other clients) by the server. A client can request general information about a font (for example, the font ascent) and the space a specific string takes when drawn with a specific font.