ri - 1:2.5.1 main

ri is a command line tool that displays descriptions of built-in Ruby
methods, classes, and modules. For methods, it shows you the calling
sequence and a description. For classes and modules, it shows a
synopsis along with a list of the methods the class or module
implements.
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This package provides ri command and descriptions about Ruby.
This package provides the ri documentation for the Ruby standard library.
The ri executable itself is in the ruby package.
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This package is a dependency package, which depends on Debian's default Ruby
version (currently v2.5).