Phosphorus is of course a chemical. When it is used as a weapon, rather than as a means of camouflage it is a chemical weapon. There are very strong grounds for thinking it was in fact used as an anti-personnel weapon in Gaza.

If so, this was a war crime, as it would have been if it had been used in the same way by anyone - Hamas, the British Army. Or the IDF.

The crucial distinction is not whether a chemical falls within a particular list of prohibited substances, but what it does, and what are the intentions of those using it, included known and anticipated "collateral damage" when used on a civilian target.