17. A conformance testing system, comprising: a sequence verifier stored in a non-transitory computer-readable medium; and a processor configured to execute instructions stored in the medium that cause the sequence verifier to: receive a plurality of messages exchanged between two or more participants; and test conformance of each of the plurality of messages to a specific markup language standard without using a reference implementation of the markup language standard; wherein the sequence verifier is a single module that is distinct from the two or more participants; wherein the plurality of messages comprise a first message sent from a first participant of the two or more participants to a second participant of the two or more participants and a second message sent from the second participant of the two or more participants to the first participant of the two or more participants, forming a sequence; wherein testing conformance comprises: comparing the first message in the sequence of messages exchanged between the first participant and the second participant to a valid sequence in a protocol verification graph to test conformance of the first message; and comparing the second message in the sequence of messages exchanged between the first participant and the second participant to a valid sequence in the protocol verification graph to test conformance of the second message, the sequence verifier verifying that the first message and second message conform to an appropriate message type based on a standard schema and were exchanged in a correct order based on the protocol verification graph; wherein the protocol verification graph describes constraints on a message including message sequence constraints and message type constraints, the protocol verification graph being created by analyzing an Extensible Markup Language (XML) standards specification.
17. A conformance testing system, comprising: a sequence verifier stored in a non-transitory computer-readable medium; and a processor configured to execute instructions stored in the medium that cause the sequence verifier to: receive a plurality of messages exchanged between two or more participants; and test conformance of each of the plurality of messages to a specific markup language standard without using a reference implementation of the markup language standard; wherein the sequence verifier is a single module that is distinct from the two or more participants; wherein the plurality of messages comprise a first message sent from a first participant of the two or more participants to a second participant of the two or more participants and a second message sent from the second participant of the two or more participants to the first participant of the two or more participants, forming a sequence; wherein testing conformance comprises: comparing the first message in the sequence of messages exchanged between the first participant and the second participant to a valid sequence in a protocol verification graph to test conformance of the first message; and comparing the second message in the sequence of messages exchanged between the first participant and the second participant to a valid sequence in the protocol verification graph to test conformance of the second message, the sequence verifier verifying that the first message and second message conform to an appropriate message type based on a standard schema and were exchanged in a correct order based on the protocol verification graph; wherein the protocol verification graph describes constraints on a message including message sequence constraints and message type constraints, the protocol verification graph being created by analyzing an Extensible Markup Language (XML) standards specification. 22. The conformance testing system of claim 17 , wherein the sequence verifier is to determine whether the plurality of messages comprise an acceptable number of repeated messages.