Save markdown heading collapsed states

[riyavsinha]

Description

I would like to save the collapsed state of a markdown header.

Suggested solution

Add an argument to the app.cell decorator.

@app.cell(collapsed=True)
def _(mo):
    mo.md(r"""### Setup""")
    return

Alternative

No response

Additional context

No response

[mscolnick]

I think as a first iteration, we can save to localStorage based on some unique ID of the header (filename, title, position)