Position of HPACK Dynamic Table Size Update

Hi,

I'd like to clarify the requirement of the position of HPACK Dynamic Table
Size Update.
Should it appear always at the beginning of the header block?  Or is it
only required to do so only if it is the ack of SETTINGS?

Background: https://github.com/summerwind/h2spec/issues/78

Best regards,
Tatsuhiro Tsujikawa