The SIP-If-Match header is used by a client (event state publisher) in
a PUBLISH request, to update previously published event state. The value is
obtained from the server in a
2xx response to a previous PUBLISH.
A server must ignore Headers that it does not understand. A proxy must not remove or modify Headers that it does not understand.
etagthe new value of the entity-tag.
java.text.ParseExceptionif the ETag syntax is invalid (not a valid token)