Tk Widget Attributes and the Resource Database
A widget attribute can be named three different ways: by its command-line option, by its resource name, and by its resource class. The command-line option is the format you use in Tcl scripts. This form is always all lowercase and prefixed with a hyphen (e.g., -offvalue). The resource name for the attribute has no leading hyphen, and it has uppercase letters at internal word boundaries (e.g., offValue). The resource class begins with an uppercase letter and has uppercase letters at internal word boundaries. (e.g., OffValue).
You need to know these naming conventions if you specify widget attributes via the resource mechanism. The command-line option can be derived from the resource name by mapping it to all lowercase. The primary advantage of using resources to specify attributes is that you do not have to litter your code with attribute specifications. With just a few resource database entries you can specify attributes for all your widgets. In addition, if attributes are specified with resources, users can provide alternate resource specifications in order to override the values supplied by the application. For attributes like colors and fonts, this feature can be important to users. Resource specifications are described in detail in Chapter 28.
The Tk Manual Pages
This book provides summaries for all the Tk commands, the widget attributes, and the default bindings. However, for the absolute truth, you may need to read the on-line manual pages that come with Tk. They provide a complete reference source for the Tk commands. You should be able to use the UNIX man program to read them:
% man button
The tkman program provides a very nice graphical user interface to the UNIX manual pages. On the Macintosh platform, the manual pages are formatted into HTML documents that you can find in the HTML Docs folder of the Tcl/Tk distribution. On Windows, the manual pages are formatted into Help documents. You can find the manual pages on the web at:
There are a large number of attributes that are common across most of the Tk widgets. These are described in a separate man page under the name options. Each man page begins with a STANDARD OPTIONS section that lists which of these standard attributes apply, but you have to look at the options man page for the description. In contrast, the tables in this book always list all widget attributes.