Trying to import soap envelope to xsd giving error

[Heucles]

When I try to add the following line to my xsd file in order to import the envelope namespace:
<xs:import namespace="http://schemas.xmlsoap.org/soap/envelope/" schemaLocation="http://schemas.xmlsoap.org/soap/envelope/"/>
It gives me the following messages:
I/O warning : failed to load external entity "http://schemas.xmlsoap.org/soap/envelope/"
and
[ { Error: Element '{http://schemas.xmlsoap.org/soap/envelope/}Envelope': No matching global declaration available for the validation root. domain: 17, code: 1845, level: 2, column: 0, line: 2 } ]
which seems normal considering the message above.

But the first one doesn´t make sense to me, it should be able to import that namespace, right?
The node version is 8.4.0 and the node-libxml-xsd version is: 1.11.4