RSpec tagging syntax with numbers fail

explanation.txt

In the example, I can run:

$> rspec . --tag "2" 

or 

$> rspec . --tag 2 

and it will find the test I want.  The others are unreachable via tag.

rspec_example.rb

describe 'Tagging syntax' do
  it 'doesnt let me use numbers', 1 => true do
    'foo'.should == 'foo'
  end

  it 'lets me use numbers as strings in symbols - yuck', :"2" => true do
    'I hate'.should_not == 'this'
  end

  it 'does not let me use numbers in strings', '3' => true do
    'bar'.should == 'bar'
  end
end