I have just posted a tutorial on my blog about writing your own template
handling plugins. It takes you through creating a template handler that
renders a hash in a view file, as an HTML table.
Perhaps a silly example, but it gets the point across simply.
I wrote this because I was searching for info on template handlers
before I wrote the .flexi handler for FlexImage and, sadly, I found
nothing. I had to resort to reverse engineering other template plugins.
Hope it helps someone.
Happy Template Handling!