- [x] set markdown from localStorage `ref.current.getInstance().setMarkdown("# rahul\n")`
- [x] to change style `ref.current.getInstance().changePreviewStyle("tab")`
- [x] reset `ref.current.getInstance().reset()`
- [x] html to markdown `ref.current.getInstance().setHTML('

Hi,testing

')`
- [x] place holder `ref.current.getInstance().setPlaceholder('# This is heading\nThis is description!')`
- [x] API https://nhn.github.io/tui.editor/latest/

Review the checked API examples in the issue and the linked TUI Editor API documentation first. No repository file or test is named, so clarify where these examples belong and which API coverage is expected; done means the requested API documentation is added or updated and the examples remain accurate.

Written by the indexing model from the issue text.