We mentioned LaTeX templates in Section 6.10. You can also specify a custom HTML template for Pandoc to convert Markdown to HTML. Below is a brief example template:

    1. <html>
    2.   <head>
    3.     <title>$title$</title>
    4.     $for(css)$
    5.     <link rel="stylesheet" href="$css$" type="text/css" />
    6.     $endfor$
    7.   </head>
    8.   <body>
    9.   $body$
    10.   </body>
    11. </html>

    You can see that the template contains a few variables such as $title$ and $body$. You can find the full list of Pandoc variables and their meanings at https://pandoc.org/MANUAL.html#templates.

    The template gives you the ultimate power to customize the HTML output. For example, you can include arbitrary CSS stylesheets or JavaScript code or libraries in the <head> area. For example, we could use a Boolean variable draft to indicate whether the document is a draft or a final version:

    1. <head>
    2. <style type="text/css">
    3. .logo {
    4.   float: right;
    5. }
    6. </style>
    7. </head>
    9. <body>
    10. <div class="logo">
    11. $if(draft)$
    12. <!-- use draft.png to show that this is a draft -->
    13. <img src="images/draft.png" alt="Draft mode" />
    14. $else$
    15. <!-- insert the formal logo if this is final -->
    16. <img src="images/logo.png" alt="Final version" />
    17. $endif$
    18. </div>
    20. $body$
    21. </body>

    Then we can set the variable draft to true or false in the YAML metadata of the Rmd document, e.g.,

    1. ---
    2. title: "An Important Report"
    3. draft: true
    4. ---

    To apply a template to an Rmd document, you can save the template to a file, and pass the file path to the template option of html_document, e.g.,

    1. output:
    2.   html_document:
    3.     template: my-template.html

    The rmarkdown package uses a custom HTML template shipped with the package, which is different from Pandoc’s default template. To use the latter, you can specify template: null.