@kapteinb: >With nothing

>With nothing to gain from such an attack

That's not really true. Chlorine gas is a very well suited tool for rooting out enemies hiding in basements, underground bunkers, and tunnels. Chemical weapons would make the inevitable victory quicker and with lower casualties (for the government forces).

The government also had very little to lose from using chemical weapons. Indications are they've done so several times before, usually with no consequences. At worst they risker another strike along the lines of the 2017 Shyrat missile strike.