Explain how to create a custom Liquid filter in Jekyll to convert text to uppercase. Include details on where the Ruby code for the filter should be placed, the basic structure of the filter's Ruby code, and provide an example of how to use this custom filter within a Liquid template on a Jekyll site.
Navigate to the Jekyll documentation. Locate and navigate to the 'Plugins' section. From the 'Plugins' section, find and navigate to the 'Filters' guide. Follow the link to the 'Liquid docs' for detailed information on creating custom Liquid filters. Extract the necessary information regarding filter code structure, file location, and usage in Liquid templates.
Explain that custom filters are typically placed in Ruby files within the `_plugins` directory of the Jekyll site. Provide a Ruby code example for an uppercase filter, demonstrating a module and method structure (e.g., `module Jekyll::CustomFilters; def uppercase(input); input.to_s.upcase; end; end;` and `Liquid::Template.register_filter`). Show how the uppercase filter would be used in a Liquid template (e.g., `{{ 'text' | uppercase }}`).