It took me some time to understand the following:
the -b option of tidy says:
> strip out smart quotes and em dashes, etc. (bare: yes)
> This option specifies if Tidy should strip Microsoft specific HTML from
> Word 2000 documents, and output spaces rather than non-breaking spaces
> where they exist in the input.
this is misleading because using the 'bare' option in php5-tidy
effectively strip out ’ but I didn't expected this after the reading of the quickref.