0.1. Syntax: Balanced plus signs (from 1 to 5)
1. Title Level 1
1.1. Title Level 2
1.1.1. Title Level 3
1.1.1.1. Title Level 4
1.1.1.1.1. Title Level 5
1.2. Label: Between brackets, alphanumeric [A-Za-z0-9_-]
2. Title Level 1
2.1. Title Level 2
2.1.1. Title Level 3
2.1.1.1. Title Level 4
2.1.1.1.1. Title Level 5
2.2. Syntax: Spaces around and/or inside are allowed (and ignored)
2.2.1. Title Level 3
2.2.2. Title Level 3
2.2.3. Title Level 3
2.2.4. Title Level 3
2.2.5. Title Level 3
2.2.6. Title Level 3
2.3. Invalid: Unbalanced plus signs
+Not Title
++Not Title+
+++Not Title++++
2.4. Invalid: Level deeper than 5
++++++Not Title 6++++++
+++++++Not Title 7+++++++
2.5. Invalid: Space between title and label
+Not Title+ [label1]
2.6. Invalid: Space inside label
+Not Title+[ label ]
2.7. Invalid: Strange chars inside label
+Not Title+[la/bel]