Rendering Process

For any Jekyll site, a build session consists of discrete phases in the following order — setting up plugins, reading source files, running generators, rendering templates, and finally writing files to disk.

While the phases above are self-explanatory, the one phase that warrants dissection is the rendering phase.

The rendering phase is further divisible into three optional stages. Every file rendered, passes through one or more of these stages as determined by the file’s content string, front matter and extension. The stages are akin to an assembly line, with the output from a stage being the input for the succeeding stage:

• Interpreting Liquid expressions in the file
  This stage evaluates Liquid expressions in the current file. By default, the interpretation is shallow — in that any Liquid expression in resulting output is not further interpreted. Moreover, any Liquid expression in the file’s front matter is left untouched.
• Unleashing the converters
  This stage invokes the converter mapped to the current file’s extension and converts the input string. This is when Markdown gets converted into HTML and Sass / Scss into CSS or CoffeeScript into JavaScript, etc, etc. Since this stage is determined by the file’s extension, Markdown or Sass inside a .html file will remain untouched.
• Populating the layouts
  By this stage, the source file is considered rendered and it will not be revisited. However, based on the file’s extension and consequently based on the front matter, it is determined whether to take the output string from the preceding stage and place into layouts or not. Whereas output from Sass files or CoffeeScript files are never placed into a layout, regular text output can go either ways based on whether a layout has been assigned via the front matter.
  
  Placement into layouts work similar to how Russian dolls encase the smaller ones within itself or how an oyster generates a pearl — the converted output from the preceding stage forms the core and layout(s) are successively rendered separately onto the core.