solvent choice controls isomer produced?

[xxxxx]

i recall reading somewhere that when hcl is added to a double bond in ethyl ether the addition is 88% "syn" and in nitromethane the addition is 100% "anti". dichloromethane is somewhere intermediate between these two. what do these terms "syn" and "anti" mean? does it mean the sterochemistry of the product can be controlled by the solvent choice?

[Rhodium]

The stereochemistry will not be affected, but the regioselectivity will. Depending on the mechanism you may end up with different diastereomers but not different enantiomers.

Addition of a halogen (X₂) to an alkene to give a di-haloalkane can be either syn- (yielding the cis-dihaloalkane) or anti- (giving the trans-dihaloalkane).