Inline

This lets you insert native DOT commands into your graph and keep it indented corectly.

graph g {
    inline 'node [shape="rect";]'
    edge a,b,c,d,a        
}

If you don't care about the format of the generated DOT file, you could just use normal strings.

graph g {
    'node [shape=rect]'
    edge a,b,c,d,a        
}

The only thing the inline command does is place proper indentation into the output. Both of those will render this final image:

The inline command was added so more advanced GraphViz users don't feel limited by the subset of implemented features.