I'll post just the opening paragraphs from the sitrep/analysis, which includes a wonderfully clear map of the four 'official' de-escalation zones. Click on the map image to enlarge it.
The strategy behind the de-escalation zones
April 21, 2018
Sic Semper Tyrannis
The recent advances by the R+6 in Ghouta, Yarmouk, Qalamun and beyond have laid bare the true strategy of the de-escalation zones established by the Astana Accords. They certainly were not meant to establish a new status quo of rebel safe areas guaranteed to torment Damascus for years to come. They are, I contend, a blueprint for ending the armed resistance to Damascus and reestablishing the territorial integrity of Syria west of the Euphrates. The eventual Turkish-Syrian border will remain a question for future resolution, one way or another.
The reduction of the Ghouta pocket, or de-escalation zone 3 as it was referred to at Astana, was a perfect example of the de-escalation strategy, a strategy to limit the death, destruction and suffering to a minimum while still attaining R+6 objectives.
It is a strategy carefully planned and executed to avoid attrition warfare. It begins with an offer/ultimatum to the rebels. You can reconcile with Damascus or be bussed to the Idlib area. If you choose Idlib you will leave all heavy weapons and vehicles to the SAA. If you refuse this offer, the R+6 will unleash a massive punch of artillery and air power followed by a violent strike by elite SAA units. This cycle is repeated until the targeted rebels surrender, reconcile or fall in defeat. This strategy saves civilian lives and infrastructure and preserves SAA combat forces.
This is how the Ghouta pocket was reduced, piece by piece. As that battle wound down, pressure was kept on the Yarmouk pocket while the Tiger Force moved to Qalamun. That battle just ended with another victory for the R+6. It appears the SAA captured a battalion worth of older but serviceable main battle tanks (or more) along with much other equipment and ammunition. Damascus has also gained additional forces for their NDF units from reconciled rebels.
With the Qalamun pocket eliminated, the Tiger Force now is reported to be moving to Yarmouk to assist in the reduction of that pocket. Some of the rebels and even some Daesh elements already took the offer for bus tickets to Jarabulus after a savage artillery and air strike followed by a quick, savage advance by the SAA 4th Mechanized Division and the Liwa al-Quds Brigade. It’s just a matter of time [before] the last of the Daesh holdouts are no more.