Ways to detect that XXXX in JSON \uXXXX does not correspond to a Unicode character?

[Costello, Roger L.]

Hi Folks,

The JSON specification says that a character may be escaped using this 
notation: \uXXXX    (XXXX are four hex digits)

However, not every four hex digits corresponds to a Unicode character. 

Are there tools to scan a JSON document to detect the presence of \uXXXX, where 
XXXX does not correspond to any Unicode character?

/Roger