Add inlineStyle matcher for sourcing block attributes

docs/block-api/attributes.md

@@ -77,6 +77,26 @@ _Example_: Extract child nodes from a paragraph of rich text.
 // }
 ```
 
+### `styleProperty`
+
+Use `inlineStyle` to extract a value from the inline style declaration of the matched element.
+
+_Example_: Extract the width value from the an inline style
+
+```js
+{
+	width: {
+		type: 'string',
+		source: 'inlineStyle',
+		selector: 'div',
+		styleProperty: 'width'
+	}
+}
+// {
+//   "width": "20px" 
+// }
+```
+
 ### `query`
 
 Use `query` to extract an array of values from markup. Entries of the array are determined by the selector argument, where each matched element within the block will have an entry structured corresponding to the second argument, an object of attribute sources.

packages/blocks/src/api/parser.js

@@ -112,6 +112,11 @@ export function matcherFromSource( sourceConfig ) {
 			return children( sourceConfig.selector );
 		case 'node':
 			return node( sourceConfig.selector );
+		case 'inlineStyle':
+			return flow( [
+				prop( sourceConfig.selector, `style.${ sourceConfig.styleProperty }` ),
+				( value ) => value !== '' ? value : undefined,
+			] );
 		case 'query':
 			const subMatchers = mapValues( sourceConfig.query, matcherFromSource );
 			return query( sourceConfig.selector, subMatchers );
@@ -164,6 +169,7 @@ export function getBlockAttribute( attributeKey, attributeSchema, innerHTML, com
 		case 'text':
 		case 'children':
 		case 'node':
+		case 'inlineStyle':
 		case 'query':
 		case 'tag':
 			value = parseWithAttributeSchema( innerHTML, attributeSchema );

packages/blocks/src/api/test/parser.js

@@ -137,7 +137,7 @@ describe( 'block parser', () => {
 	} );
 
 	describe( 'parseWithAttributeSchema', () => {
-		it( 'should return the matcher’s attribute value', () => {
+		it( 'should return the matcher’s text content value', () => {
 			const value = parseWithAttributeSchema(
 				'<div>chicken</div>',
 				{
@@ -149,6 +149,19 @@ describe( 'block parser', () => {
 			expect( value ).toBe( 'chicken' );
 		} );
 
+		it( 'should return the matcher’s style property value', () => {
+			const value = parseWithAttributeSchema(
+				'<div style="width: 10px">chicken</div>',
+				{
+					type: 'string',
+					source: 'inlineStyle',
+					selector: 'div',
+					styleProperty: 'width',
+				},
+			);
+			expect( value ).toBe( '10px' );
+		} );
+
 		it( 'should return the matcher’s string attribute value', () => {
 			const value = parseWithAttributeSchema(
 				'<audio src="#" loop>',
@@ -216,7 +229,7 @@ describe( 'block parser', () => {
 			expect( value ).toBe( 10 );
 		} );
 
-		it( "should return the matcher's attribute value", () => {
+		it( "should return the matcher's text content value", () => {
 			const value = getBlockAttribute(
 				'content',
 				{
@@ -230,6 +243,21 @@ describe( 'block parser', () => {
 			expect( value ).toBe( 'chicken' );
 		} );
 
+		it( "returns the matcher's style property value", () => {
+			const value = getBlockAttribute(
+				'content',
+				{
+					type: 'string',
+					source: 'inlineStyle',
+					selector: 'div',
+					styleProperty: 'width',
+				},
+				'<div style="width:10px">chicken</div>',
+				{}
+			);
+			expect( value ).toBe( '10px' );
+		} );
+
 		it( 'should return undefined for meta attributes', () => {
 			const value = getBlockAttribute(
 				'content',