add styles to state diagram transitions

[clambert]

I am currently trying to create the same state diagram in multiple places. Each version highlights one state transition and its corresponding states. This will be used to explain the transition process. I can uniquely identify the states in question by changing their background colors (fill). However I would like to make the transition arrow and its corresponding description text bold. At this point the best I have to go off of is the CSS class edgeLabel. If there were a syntax similar to:

stateA className -->:::transitionClassName stateB : transition description

This would allow for a way to style a specific transition using the classDef transtionClassName. In my case I just want to identify the state as bold with stroke-width and font-weight. I'm not saying do it this way specifically, but the example would be consistent.

[pierre-haessig]

This would be useful as well for controlled Markov chains (e.g. used in Reinforcement Learning/MDPs), to highlight the transitions due to the choice of actions.