Subgraphs for ClassDiagrams

[jcurtis-cc]

Proposal

It's useful to be able to make sections of class diagrams visually distinct in the same manner as subgraph is used for flowcharts. Applying this to class diagrams is common in other UML languages.

Example

classDiagram
direction RL

%% create graph edges
AbstractExpression <--o `Client Application` : aggregates
`Client Application` --> `Context` : uses

%% create a subgraph like in a flowchart
subgraph ast ["Abstract Syntax Tree"]
TerminalExpression --|> AbstractExpression : extends
NonTerminalExpression --|> AbstractExpression : extends
NonTerminalExpression o--> AbstractExpression : aggregates
end

%% create subgraph edge to node outside subgraph
ast -->  `Context` : uses

%% create class definitions
class AbstractExpression{
    +interpret()
}
class TerminalExpression{
    +value
    +interpret()
}
class NonTerminalExpression{
    +left
    +right
    +interpret()
}

Screenshots

[jgreywolf]

Dupe of #3384