Puppet users - Mar 2014 - resource title is unique for each instance. what about resource name?

as explained here: 
http://docs.puppetlabs.com/puppet/latest/reference/lang_defined_types.html#title-and-name
resource *title* is guaranteed to be unique for each instance.

I thought that resource *name* was not required to be unique.
however this code suggests the opposite:

my_resource { r1:
  name => 'r'
}

my_resource { r2:
  name => 'r'
}

define my_resource {
}

$ puppet apply test.pp
Error: Puppet::Parser::AST::Resource failed with error ArgumentError: 
Cannot alias My_resource[r2] to ["r"] at /private/tmp/a.pp:7; resource
["My_resource", "r"] already declared at /private/tmp/a.pp:3
at
/private/tmp/a.pp:7 on node mac4c.local


so, is resource *name* also unique for each instance?

where is it explained?
I do not see this info on the documentation:
http://docs.puppetlabs.com/puppet/latest/reference/lang_defined_types.html#title-and-name


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