Why is File.read('/path/to/file') not in Ruby docs?

Question

Why is the File.read method not documented in http://ruby-doc.org/core-2.3.3/File.html when it clearly exists:

$ irb
irb(main):001:0> File.read('readme.md')
=> "hello world"

Answer 1

It is documented:

http://ruby-doc.org/core-2.3.3/IO.html#method-c-read

The method is inherited from IO though.

Answer 2

Use Ruby to investigate:

File.methods.include? :read
 #=> true 
File.methods(false).include? :read                                                                    
 #=> false 
File.ancestors
 #=> [File, IO, File::Constants, Enumerable, Object, Kernel, BasicObject] 
IO.methods(false).include? :read
 #=> true