Deprecation: #81686 - Accessing core TypoScript with .txt file extension has been deprecated 

See forge#81686

Description 

TYPO3 Core TypoScript files were renamed from .txt extension to .typoscript and .tsconfig. The backward compatibility layer has been introduced for <INCLUDE_TYPOSCRIPT inclusion. If including file with .txt does not exist, then TYPO3 will try to load a file with .typoscript extension.

Impact 

Installations including Core TypoScript using old file extension will trigger a PHP E_USER_DEPRECATED error.

Migration 

Rename file name from .txt to .typoscript extension. For example code like:

<INCLUDE_TYPOSCRIPT: source="FILE:EXT:form/Configuration/TypoScript/setup.txt">
<INCLUDE_TYPOSCRIPT: source="FILE:EXT:fluid_styled_content/Configuration/TypoScript/constants.txt">
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should be changed to:

<INCLUDE_TYPOSCRIPT: source="FILE:EXT:form/Configuration/TypoScript/setup.typoscript">
<INCLUDE_TYPOSCRIPT: source="FILE:EXT:fluid_styled_content/Configuration/TypoScript/constants.typoscript">
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