Parser Plugins - Open & Closing Tag Usage

Hi,
I am trying to create some custom parser plugins within a module I am working on.
I have single tag plugins with or without parameters functioning fine.
However, when I try to use opening and closing plugin tags the closing tags line is rendered in the output. I am also unsure how to access the content within the tags from withing my plugin function.
The documentation for parser plugins is fairly sparce. Any examples of an open and closing tag plugin functions would be much appreciated.