None are valid emphasis without spaces.
Escaped asterisks * should * be ignored by MD037.
Escaped asterisks * should * be ignored by MD037.
Escaped asterisks * should * be ignored by MD037.
Escaped underscores _ should _ be ignored by MD037.
Escaped underscores _ should _ be ignored by MD037.
Escaped underscores _ should _ be ignored by MD037.
All could be reported because they are valid single-character marker emphasis when no spaces are present.
Escaped asterisks ** should ** be ignored by MD037.
Escaped asterisks ** should ** be ignored by MD037.
Escaped underscores __ should __ be ignored by MD037.
Escaped underscores __ should __ be ignored by MD037.
All should be reported, but are ignored because they look like the start of an embedded emphasis.
Escaped asterisks ** should ** be ignored by MD037.
Escaped asterisks ** should ** be ignored by MD037.
Escaped underscores __ should __ be ignored by MD037.
Escaped underscores __ should __ be ignored by MD037.