How to conceal the "#" markdown symbol?

1. I want to conceal the "#" markdown symbol in all cases except when I start to edit the header line like the Typora style?

2. What's the <ac> symbol in the toc buffer like the screenshot below and how to remove it?

https://groups.google.com/group/pandoc-discuss/attach/113699c84bafcf/TIM%E6%88%AA%E5%9B%BE20190118145234.png?part=0.1&view=1&authuser=0

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