Difference between Custom Intents and App Intents

Hi everyone. Can someone explain the difference between custom intents and app intents, and provide documentation for the type of intent needed to create a shortcut from an installed app with the same functionality as the manual "repeat text" shortcut created on my phone which listens for speech and repeats it using Siri speakers?

Difference between Custom Intents and App Intents
 
 
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