Markdown reader: allow more attributes in special spans

Spans with "smallcaps" as the first class are converted to *SmallCaps*
elements. While previously no other classes or attributes were allowed,
additional classes, attributes, and an identifier are not permitted and
kept in a *SmallCaps* wrapping *Span* element.

The same change is applied to underline spans, where the first class
must be either "ul" or "underline".

Closes: #4102

1 files changed, 11 insertions, 0 deletions

diff --git a/test/command/4102.md b/test/command/4102.md
new file mode 100644
index 000000000..88e2a4ddb
--- /dev/null
+++ b/test/command/4102.md
@@ -0,0 +1,11 @@
+SmallCaps spans can have additional attributes.
+```
+% pandoc -t latex -f markdown
+[Populus]{.smallcaps lang=la}
+
+[Romanus]{.smallcaps}
+^D
+\foreignlanguage{latin}{\textsc{Populus}}
+
+\textsc{Romanus}
+```