My question comes from not understanding how BIP 144 works? Regarding the BIP what I ask is, whether legacy nodes support the new parser, so that they treat Segwit tranasctions as valid? There it is stated:
Parsers supporting this BIP will be able to distinguish between the old serialization format (without the witness) and this one. The marker byte is set to zero so that this structure will never parse as a valid transaction in a parser that does not support this BIP. If parsing were to succeed, such a transaction would contain no inputs and a single output.
In relation to my main question, I could not understand how legacy nodes treat the witness fields of a segwit transaction?