Add support for rendered description

The description supports markdown inlines.

_extensions/quarto-ext/lightbox/_extension.yml

@@ -1,6 +1,6 @@
 title: Lightbox
 author: RStudio, PBC
-version: 0.1.4
+version: 0.1.5
 quarto-required: ">=1.2.198"
 contributes:
   filters:

_extensions/quarto-ext/lightbox/lightbox.lua

@@ -8,8 +8,9 @@ local needsLightbox = false
 local imgCount = 0
 
 -- attributes to forward from the image to the newly created link
+local kDescription = "description"
 local kForwardedAttr = {
-  "title", "description", "desc-position", 
+  "title", kDescription, "desc-position", 
   "type", "effect", "zoomable", "draggable"
 }
 
@@ -20,6 +21,17 @@ local kGalleryPrefix = "quarto-lightbox-gallery-"
 -- A list of images already within links that we can use to filter
 local imagesWithinLinks = pandoc.List({})
 
+local function readAttrValue(el, attrName) 
+  if attrName == kDescription then
+    local doc = pandoc.read(el.attr.attributes[attrName])
+    local attrInlines = doc.blocks[1].content
+    return pandoc.write(pandoc.Pandoc(attrInlines), "html")
+  else 
+    return el[attrName]
+  end
+
+end
+
 return {
   {
     Meta = function(meta) 
@@ -137,8 +149,8 @@ return {
         for i, v in ipairs(kForwardedAttr) do
           if imgEl.attr.attributes[v] ~= nil then
             -- forward the attribute
-            linkAttributes[v] = imgEl.attr.attributes[v]
-
+            linkAttributes[v] = readAttrValue(imgEl, v)
+          
             -- clear the attribute
             imgEl.attr.attributes[v] = nil
           end

example.qmd

@@ -11,7 +11,7 @@ Here is a simple image with a description. This also overrides the
 description position and places it to the left of the image.
 
 ![Beach in
-Chilmark](images/mv-0.jpg){description="Chilmark has a reputation as having some of the best beaches on Martha's Vineyard. Chilmark beaches are resident only in the summer, so be sure to have your proof of residency ready if you'd like to visit one of these special places."
+Chilmark](images/mv-0.jpg){description="Chilmark has a reputation as having some of the best beaches on Martha's Vineyard. Chilmark beaches are resident only in the summer, so be sure to have your proof of residency ready if you'd like to visit one of these special places. _credit:_ [Chilmark Beach](https://unsplash.com/photos/VBDJGOMCwps)"
 desc-position="left"}
 
 ## Elsewhere