Add require()

Author: cwickham

docs/extensions/lua-api.qmd

@@ -72,6 +72,37 @@ function Div(el)
 end
 ```
 
+### `require()`
+
+In larger, more complex filters, it becomes useful to structure your Lua code in modules.
+Quarto overwrites the standard LUA `require()` to support the use of relative paths, 
+so that small modules can be easily created and reused.
+
+For example:
+
+```{.lua filename="filter.lua"}
+local utility = require('./utils')
+function Pandoc(doc)
+  -- process 
+end
+```
+
+Using relative paths makes it harder for multiple filters to accidentally
+create conflicting module names (as would eventually happen when using the standard Lua
+`require('utils')` syntax). It's possible to refer to subdirectories and parent directories as well:
+
+```{.lua filename="filter2.lua"}
+local parsing = require('./utils/parsing')
+function Pandoc(doc)
+  -- process 
+end
+```
+
+```{.lua filename="utils/parsing.lua"}
+local utils = require("../utils")
+-- ...
+```
+
 ### Format Detection
 
 Extensions will often need to detect the current format to create custom content depending on the target output medium. The `quarto.doc.is_format()` function