Warnings which are raised during the recognition task.
In general character recognition processes do not really either
fail or succeed. It is true that sometimes they are more successful
than others, that sometimes things run smoothly, that sometimes
they hit problems. However it is quite normal to find that parts of
a document can be recognized fairly well but that other parts are
In the event of an exceptional failure ABCpdf will indeed throw
an exception. However if it simply hits some rough patches but
manages to extract a useful amount of text then any problems will
be reported via this property rather than via an exception.