the definition of smoke used was too restrictive - smoke is not just gases. i have borrowed from wikipedia, which seemed to have the most useful and succinct definition of smoke.

i also changed i.e. to e.g. because ie means 'that is' and what is clearly intended is 'for example' or exempli gratia = eg.

on the matter of commas in abbreviations, there is lively debate online, and it does seem that the chicago style of e.g. is being slowly replaced either by no commas at all or just one comma at the end. one thinks of USA, GB, etc. i have stuck with chicago style as that is what the existing author has used. in the style guide for blender docs i did not see any reference to chicago or any other external style guide. maybe i missed it. if there is such a reference, i would be grateful to know where it was.