Add vars from #4499

Author: cwickham

docs/extensions/lua-api.qmd

@@ -103,6 +103,30 @@ local utils = require("../utils")
 -- ...
 ```
 
+### Document Metadata
+
+Extensions may need to access the path for the input and output files. 
+Quarto makes these variables available:
+
+| Function                 | Description                                      |
+|--------------------------|--------------------------------------------------|
+| `quarto.doc.input_file`  | Full path to input file for the current render.  |
+| `quarto.doc.output_file` | Full path to output file for the current render. |
+
+### Project Metadata
+
+Extensions may need to know about paths relevant to the project.
+Quarto makes these variables available:
+
+
+| Function                          | Description                                                                                                     |
+|-----------------------------------|-----------------------------------------------------------------------------------------------------------------|        
+| `quarto.project.directory`        | Full path to current project directory (`nil` if no project).                                                   |
+| `quarto.project.output_directory` | Full path to current project output directory (`nil` if no project).                                            |
+| `quarto.project.offset`           | Offset (relative path) from the directory of the current file to the root of the project (`nil` if no project). |
+| `quarto.project.profile`          | List of currently active project profiles.                                                                      |
+
+
 ### 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