Typically, the application implements object information dialogs that let you view and edit metrical data and object attributes. These dialogs show up when you double-click an object. There are several flavours of object information dialogs
The multiple objects variant must have an extra checkbox for each object attribute in the dialog. When the dialog is confirmed and the checkbox is set, the value entered for the attribute is applied to all objects in the selection.
Implementation of object information dialogs is left to the application developer (for example code see the EDtCEvent method in DemoCAD).