Markdown title in code cell

cell_title.py

## Add this text to the top of your notebook to define '%title' magic.
## Use it to put an H3 title in the cell output, with the title shown
## in the JupyterLab Table-of-Contents sidebar:
##     %title Cell title $some_local_variable
from IPython.core.magic import register_line_magic
@register_line_magic
def title(msg):
    """Add a markdown title (level 3) to the current cell output stream."""
    from IPython.display import display, Markdown
    display(Markdown("### "+msg))
del register_line_magic, title