Markdown implementations differ in the way white space interacts with headings. The CommonMark specification does not require an empty line before and after a heading. On the other hand, by default mdview ends a heading only when it finds an empty line. This is an extension (and it can be disabled). Under the extension, contiguous lines are joined together to form the heading. Two spaces at the end of a heading line become a hard line-break.
See also heading examples.
See the hard line-break test file.
TEST atx-style heading continuation (extension)...
RESULT three headings comprising two lines each.
TEST settext-style heading continuation (extension)...
RESULT two headings comprising two lines each.