As we have already said, despite models, you can create your own Processing scripts using the Python programming language. Basically, Processing script is Python code plus some additional metadata required by Processing.
Every Processing script starts with a special block of metadata. This information is needed by Processing to register a script as an algorithm and use it from the toolbox, modeler, and so on. Each metadata entry is placed on a new line, starting with the double Python comment symbol (
##), and has the following structure:
element_name = element_type [optional_parameters]
Metadata items can be divided into three groups: items that describe the script, items that describe script input, and items that describe ...