Drscheme’s capability interface provides a mechanism for tools to allow languages to hide their GUI interface, if the tool does not apply to the language. Tools register capabilities keyed with symbols via. drscheme:language:register-capability. Once registered, a tool can query a language, via the capability-value method. The result from this method controls whether or not the tool shows this part of the GUI for DrScheme.
See drscheme:language:register-capability for a list of the capabilities registered by default.