Can not open .md file via AppleScript on macOS 10.14

On macOS 10.14.6, MacDown can not open .md file via AppleScript's open command.

So, I rewote your MacDown.sdef file to...

Then this script works.

set aFile to choose file of type {"net.daringfireball.markdown"}

tell application "MacDown"
open aFile
end tell

Inspect MacDown.sdef and compare its open command with the definition shown in the issue. Run the supplied AppleScript on macOS 10.14.6 and confirm that choosing a Markdown file opens it in MacDown through AppleScript.

Written by the indexing model from the issue text.