Hi :),

I just faced an issue where adhoc created attributes where allways being quoted SingleQuote despite having QuoteType set to DoubleQuote as described in #552
When looking at the code I realized some inconsistencies in the behavior of InternalQuoteType vs QuoteType.
As such here is my proposed behavior for these properties:

1. InternalQuoteType is the QuoteType inferred by the system when reading the document or on Value set ( ex: Value being set for atribute with WithoutValue )
2. QuoteType is the value set by the user that overrides the Internal calculated value, except if the value is being set to Initial wich rolls back the QuoteType to the internal value

With this behavior I believe we can have a consistent and intuitive way of handling quotes in attributes
All public behavior of the classes was kept untouched so there should not be any breaking change ( ex: Global setting in the document still overrides any of these attributes )

Please consider this change since I believe it fixes #552 and #516 and makes attribute quoting much more intuitive.

Thanks and best regards
POFerro