Pattern content only experiment: Make template parts section blocks (WordPress#71627)

* Make template parts contentOnly by default when using contentOnly pattern experiment
* Make Site Tagline a content block

Co-authored-by: talldan <[email protected]>
Co-authored-by: jeryj <[email protected]>

Author: talldan

docs/reference-guides/core-blocks.md

@@ -900,7 +900,7 @@ Describe in a few words what this site is about. This is important for search re
 
 -	**Name:** core/site-tagline
 -	**Category:** theme
--	**Supports:** align (full, wide), color (background, gradients, text), interactivity (clientNavigation), spacing (margin, padding), typography (fontSize, lineHeight), ~~html~~
+-	**Supports:** align (full, wide), color (background, gradients, text), contentRole, interactivity (clientNavigation), spacing (margin, padding), typography (fontSize, lineHeight), ~~html~~
 -	**Attributes:** level, levelOptions, textAlign
 
 ## Site Title

packages/block-editor/src/store/private-selectors.js

@@ -519,16 +519,17 @@ export function isSectionBlock( state, clientId ) {
 	}
 
 	const attributes = getBlockAttributes( state, clientId );
+	const isTemplatePart = blockName === 'core/template-part';
 	if (
-		attributes?.metadata?.patternName &&
+		( attributes?.metadata?.patternName || isTemplatePart ) &&
 		!! window?.__experimentalContentOnlyPatternInsertion
 	) {
 		return true;
 	}
 
 	// Template parts become sections in navigation mode.
 	const _isNavigationMode = isNavigationMode( state );
-	if ( _isNavigationMode && blockName === 'core/template-part' ) {
+	if ( _isNavigationMode && isTemplatePart ) {
 		return true;
 	}
 

packages/block-editor/src/store/reducer.js

@@ -2286,6 +2286,9 @@ function getDerivedBlockEditingModesForTree(
 	const contentOnlyParents = [
 		...contentOnlyTemplateLockedClientIds,
 		...unsyncedPatternClientIds,
+		...( window?.__experimentalContentOnlyPatternInsertion
+			? templatePartClientIds
+			: [] ),
 	];
 
 	traverseBlockTree( state, treeClientId, ( block ) => {

packages/block-library/src/site-tagline/block.json

@@ -36,6 +36,7 @@
 				"text": true
 			}
 		},
+		"contentRole": true,
 		"spacing": {
 			"margin": true,
 			"padding": true,