Practical Programming in Tcl & Tk, Third Edition

Naming Tk Widgets

The period in the name of the button instance, .hello, is required. Tk uses a naming system for the widgets that reflects their position in a hierarchy of widgets. The root of the hierarchy is the main window of the application, and its name is simply a dot (i.e., .). This is similar to the naming convention for directories in UNIX where the root directory is named /, and then / is used to separate components of a file name. Tk uses a dot in the same way. Each widget that is a child of the main window is named something like .foo. A child widget of .foo would be .foo.bar, and so on. Just as file systems have directories that are containers for files and other directories, the Tk window hierarchy uses frame widgets that are containers ...