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The following changes will be made to the channel header:
Remove
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The Global Search function will be moved to the Global Header
Remove the Saved Messages Icon Button
The Saved Messages Icon Button will be moved to the Global Header
Remove the Recent Mentions Icon Button
The Recent Mentions Icon Button will be moved to the Global Header
Remove Global-level App Icons
Any app that has a global context will move to the App Bar as the new home for apps.
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