What is the source for wishing someone "תתחדש" for a new item of clothing?
See the Rema OC:224 who brings a minhag to wish someone that bought new clothes "תבלה ותחדש". Literal translation is "You should wear it out and renew it" which I would consider to be the rough equivalent of "Use it in good health". Basically you are wishing the proud owner of the new item to put it to good use.
Where did the prevalent custom to simply say "תתחדש" ("Titchadesh") come from? It simply doesn't make sense.. the word literally means - I think - "you should renew yourself". Is this another type of well-wishing (and what does it mean) or is it related to the Rema above?