Hi! I would like to know if watermarks can be updated from SDFs and propagated to other operators for windowing? As per the design docs [1] [2] it seems plausible to me as the idea behind SDFs is to replace the Source APIs and make a DoFn more generic.
[1] Splittable DoFn Proposal <https://docs.google.com/document/d/1AQmx-T9XjSi1PNoEp5_L-lT0j7BkgTbmQnc6uFEMI4c/edit#> [2] SDF API Changes <https://docs.google.com/document/d/1BGc8pM1GOvZhwR9SARSVte-20XEoBUxrGJ5gTWXdv3c/edit>
