system-of-quantities.txt

Qt property as defined by QMetaProperty:
- name
- type, typeName, userType
- is{Enum|Flag}Type
- is{Readable|Writable|Resetable}
- isConstant (same value for a given QObject instance)
- is{Designable|Scriptable}
- idStored (static vs dynamic value)
- isFinal (can't be overridden by a derived class)
- isUser (For QItemDelegate?)
- propertyIndex

Extension:
- Default value
- Physical quantity
- Default unit
- Property group
- Constraint:
 - Minimum, Maximum, Step (for GUI)
 - Decimals (for GUI)
 - Echo mode
 - Reg exp
 - ...
- Icon map (for enum)
- Documentation (Tool tip, Status tip, What's this)
- Icon

QtPropertyBrowser (http://doc.qt.digia.com/qq/qq18-propertybrowser.html):
 QtVariantPropertyManager and QtVariantProperty provide the above mentioned constraints, documentation and icon.
 
=> - Extend QtVariantPropertyManager and QtVariantProperty to support above extension
   - Choice:
     - Add a propertyManager() to DocumentObject that construct the right QtVariantPropertyManager
     - use a factory approach
     - Extend somehow QMetaProperty