Properties
Every window has a predefined set of attributes and a set of properties, all stored in the server and accessible to the clients via appropriate requests. Attributes are data about the window, such as its size, position, background color, etc. Properties are arbitrary pieces of data attached to a window. Unlike attributes, properties have no meaning at the level of the X Window core protocol. A client can store arbitrary data in a property of a window.
A property is characterized by a name, a type, and a value. Properties are similar to variables in imperative programming languages, in that a client can create a new property with a given name and type and store a value in it. Properties are associated to windows: two properties with the same name can exist on two different windows while having different types and values.
The name, type, and value of a property are strings; more precisely, they are atoms, that is, strings stored in the server and accessible to the clients via identifiers. A client application can access a given property by using the identifier of the atom containing the name of the property.
Properties are mostly used for inter-client communication. For example, the property named WM_NAME (the property named by the atom whose associated string is "WM_NAME") is used for storing the name of windows. Window managers typically read this property to display the name of windows in their title bar.
Some types of inter-client communication use properties of the root window. For example, according to the freedesktop window manager specification, window managers should store the identifier of the currently active window in the property named _NET_ACTIVE_WINDOW of the root window. The X resources, which contain parameters of programs, are also stored in properties of the root window; this way, all clients can access them, even if running on different computers.
The xprop program prints the properties of a given window; xprop -root prints the name, type, and value of each property of the root window.
Read more about this topic: X Window System Core Protocol
Famous quotes containing the word properties:
“A drop of water has the properties of the sea, but cannot exhibit a storm. There is beauty of a concert, as well as of a flute; strength of a host, as well as of a hero.”
—Ralph Waldo Emerson (1803–1882)
“The reason why men enter into society, is the preservation of their property; and the end why they choose and authorize a legislative, is, that there may be laws made, and rules set, as guards and fences to the properties of all the members of the society: to limit the power, and moderate the dominion, of every part and member of the society.”
—John Locke (1632–1704)