A collection of UPnP service state variables.

This class extends Vector to manage multiple StateVariable objects that represent the state variables of UPnP services. It provides type-safe collection management for service state tracking and event notification.

Key features:

• Type-safe state variable collection
• XML element name constant
• Vector-based implementation for efficiency
• Service state management
• Event notification integration

This class is used by UPnP services to maintain collections of state variables, enabling organized state management and event notification for service monitoring and control applications.