Added some documentation on what makes a valid URI.
Added some documentation on what makes a valid URI.

From the docs, it says,
“A URI is composed from a limited set of characters consisting of
   digits, letters, and a few graphic symbols”

refs #8368
mvdriel/cakephp,dakota/cakephp,ndm2/cakephp,cakephp/cakephp,tenkoma/cakephp,ndm2/cakephp,dakota/cakephp,petteyg/cakephp,cakephp/cakephp,ADmad/cakephp,mvdriel/cakephp,ADmad/cakephp,mvdriel/cakephp,davidyell/cakephp,garethellis36/cakephp,petteyg/cakephp,tenkoma/cakephp,CakeDC/cakephp,cakephp/cakephp,CakeDC/cakephp,dakota/cakephp,ADmad/cakephp,dakota/cakephp,ADmad/cakephp,garethellis36/cakephp,tenkoma/cakephp,CakeDC/cakephp,petteyg/cakephp,garethellis36/cakephp,CakeDC/cakephp,tenkoma/cakephp,mvdriel/cakephp,ndm2/cakephp,davidyell/cakephp,cakephp/cakephp,davidyell/cakephp,petteyg/cakephp,garethellis36/cakephp,ndm2/cakephp