How to highlight custom keywords in Quarto docs code chunks?

I’m writing a brief Quarto document where I explain some SQL clauses/keywords. I’d like to have all of those clauses to be highlighted in my code chunks, but not all of them are supported by default syntax highlighting. Is there a way to add custom keywords to syntax highlighting settings?

For example, I wrote the following code chunks:

SELECT col_name(s)
FROM tbl_name
LIMIT n OFFSET m

-- Syntax supported by MySQL, MariaDB, PostgreSQL, SQLite
-- LIMIT = number of rows to retrieve
-- OFFSET = starting row (optional) 

SELECT TOP n col_name(s)
FROM tbl_name

-- Syntax supported by SQL Server and MS Access

And i got the following outputs in my rendered document:

I want both OFFSET and TOP to be highlighted in orange, like SELECT, FROM etc. How can I do that?

Answer

There are several SQL highlight variants, you can get a list of those with quarto pandoc --list-highlight-languages and switching from sql to sqlpostgresql will get you highlighted OFFSET.

It’s surprisingly easy to customize any of the existing highlights, https://pandoc.org/MANUAL.html#syntax-highlighting points you to KDE-style XML syntax definition files, https://github.com/KDE/syntax-highlighting/tree/master/data/syntax . Pick sql.xml (or any other ) as a base and add additional keywords:

...
    <list name="keywords">
      <item>OFFSET</item>
      <item>TOP</item>
...

I also changed the name attribute (<language name="SQL_CUSTOM" ... and saved it next to Quarto qmd as sql_custom.xml, having all files in a working directory, Quarto / Pandoc picked up updated definition file once it was added to syntax-definitions list.

Sample qmd:

---
title: "custom syntax hl"
format: html
theme: solar
syntax-definitions: 
  - sql_custom.xml
editor: source
---

### sql

``` sql
SELECT col_name(s) FROM tbl_name LIMIT n OFFSET m
SELECT TOP n col_name(s) FROM tbl_name
```

### sqlpostgresql knows about `OFFSET`

``` sqlpostgresql
SELECT col_name(s) FROM tbl_name LIMIT n OFFSET m
SELECT TOP n col_name(s) FROM tbl_name
```

### sql_custom knows about `OFFSET` & `TOP`

``` sql_custom
SELECT col_name(s) FROM tbl_name LIMIT n OFFSET m
SELECT TOP n col_name(s) FROM tbl_name
```

And rendered result: