Bugfix/issue 3772 (#3905)

* only append to content if it's paragraph. Closes #3772

Author: cscheid

news/changelog-1.3.md

@@ -106,6 +106,7 @@
 - `quarto check` now supports `quarto check versions` for checking binary dependency versions in the case of custom binaries ([#3602](https://github.com/quarto-dev/quarto-cli/issues/3602)).
 - the API for shortcode handlers in lua now accepts a fourth parameter `raw_args` which hold the unparsed arguments in a table ([#3833](https://github.com/quarto-dev/quarto-cli/issues/3833)).
 - remove scaffolding div from conditional content in final output ([#3847](https://github.com/quarto-dev/quarto-cli/issues/3847)).
+- ensure proof titles are appended to paragraph nodes ([#3772](https://github.com/quarto-dev/quarto-cli/issues/3772)).
 
 ## Pandoc filter changes
 

src/resources/filters/crossref/theorems.lua

@@ -143,12 +143,15 @@ function crossrefTheorems()
               span.content:insert(pandoc.Str(")"))
             end
             tappend(span.content, { pandoc.Str(". ")})
+
+            -- if the first block is a paragraph, then prepend the title span
             if #el.content > 0 and 
-               el.content[1].content ~= nil and #el.content[1].content > 0 then
+               el.content[1].t == "Para" and
+               el.content[1].content ~= nil and 
+               #el.content[1].content > 0 then
               el.content[1].content:insert(1, span)
             else
-              -- if the first block can't handle content insertion
-              -- then insert a new paragraph
+              -- else insert a new paragraph
               el.content:insert(1, pandoc.Para{span})
             end
           end