Dear teachers...

Could you shed some light on this?

"Language is more fashion than science, and matters of usage, spelling and pronunciation tend to wander around like hemlines."

-Bill Bryson, author (b. 1951)

Nice quotation, it could not be any nicer because I am not sure I get the full meaning of it. All I get from it is 'practice makes perfect'...but... 'to wander around like hemlines' is still a mystery. How could 'hemlines' wander?

Many thanks
The length of skirts varies from season to season, "wandering" in this person's view. So also do linguistic convention and "rules" vary from generation to generation, even from area to area.
Now I get it, thanks