Title: Theory / Unimportant / CS / Descriptive / Material / Component / Top

Name: Tob app bar
Page: https://material.io/design/navigation/understanding-navigation.html#types-of-navigation
Context: Material
Definition2: contextual action bar
Example: regular
Conjdef: either
DefType: Persistent bar on top of the app

Name: Contextual action bar
Definition: provide actions for selected item. remaining active until an action is taken or it is dismissed.
Page: https://material.io/design/navigation/understanding-navigation.html#types-of-navigation
Context: Material

Name: Regular action bar
Definition: Navigation icon (optional)
Page: https://material.io/design/navigation/understanding-navigation.html#types-of-navigation
Context: Material
Definition2: Title (optional)
Definition3: action item (optional)
Definition4: Overflow menu (optional)
DefType: A non contextual action top bar. In this order

Name: navigation icon
Definition: A menu icon
Page: https://material.io/design/navigation/understanding-navigation.html#types-of-navigation
Context: Material
Definition2: an up arrow, which navigates up an app's hierarchy
Conjdef: Either
Definition3: A back arrow, which returns to the previous screen
DefType: An icon allowing some navigation in the app.

Question: What to do is text is long
Answer: use a prominent app bar and wrap the title to two lines.
Page: https://material.io/design/navigation/understanding-navigation.html#types-of-navigation
Context: Material

Question: In which order to put buttons in top app bar
Answer: Most important buttons on left, if there is too much, in overflow menu
Page: https://material.io/design/navigation/understanding-navigation.html#types-of-navigation
Context: Material

Question: What happen to the top bar when the screen scroll up
Answer: It may disappear or remain
Page: https://material.io/components/app-bars-top#behavior
Context: Material

Question: What happen to the top bar when the screen scroll down
Answer: It reappears or remains
Page: https://material.io/components/app-bars-top#behavior
Context: Material