diff --git a/src/parse/read/directives.js b/src/parse/read/directives.js
index 28adc3078a..9cc09392d7 100644
--- a/src/parse/read/directives.js
+++ b/src/parse/read/directives.js
@@ -1,19 +1,11 @@
-import { parse, parseExpressionAt } from 'acorn';
+import { parseExpressionAt } from 'acorn';
 import spaces from '../../utils/spaces.js';
 
-export function readEventHandlerDirective ( parser, start, name ) {
-	const quoteMark = (
-		parser.eat( `'` ) ? `'` :
-		parser.eat( `"` ) ? `"` :
-		null
-	);
-
-	const expressionStart = parser.index;
-
+function readExpression ( parser, start, quoteMark ) {
 	let str = '';
 	let escaped = false;
 
-	for ( let i = expressionStart; i < parser.template.length; i += 1 ) {
+	for ( let i = start; i < parser.template.length; i += 1 ) {
 		const char = parser.template[i];
 
 		if ( quoteMark ) {
@@ -21,7 +13,6 @@ export function readEventHandlerDirective ( parser, start, name ) {
 				if ( escaped ) {
 					str += quoteMark;
 				} else {
-					parser.index = i + 1;
 					break;
 				}
 			} else if ( escaped ) {
@@ -35,7 +26,6 @@ export function readEventHandlerDirective ( parser, start, name ) {
 		}
 
 		else if ( /\s/.test( char ) ) {
-			parser.index = i;
 			break;
 		}
 
@@ -44,13 +34,25 @@ export function readEventHandlerDirective ( parser, start, name ) {
 		}
 	}
 
-	const ast = parse( spaces( expressionStart ) + str );
+	const expression = parseExpressionAt( spaces( start ) + str, start );
+	parser.index = expression.end;
 
-	if ( ast.body.length > 1 ) {
-		parser.error( `Event handler should be a single call expression`, ast.body[1].start );
-	}
+	parser.allowWhitespace();
+	if ( quoteMark ) parser.eat( quoteMark, true );
 
-	const expression = ast.body[0].expression;
+	return expression;
+}
+
+export function readEventHandlerDirective ( parser, start, name ) {
+	const quoteMark = (
+		parser.eat( `'` ) ? `'` :
+		parser.eat( `"` ) ? `"` :
+		null
+	);
+
+	const expressionStart = parser.index;
+
+	const expression = readExpression( parser, expressionStart, quoteMark );
 
 	if ( expression.type !== 'CallExpression' ) {
 		parser.error( `Expected call expression`, expressionStart );
@@ -127,3 +129,29 @@ export function readBindingDirective ( parser, start, name ) {
 		value
 	};
 }
+
+export function readTransitionDirective ( parser, start, name, type ) {
+	const quoteMark = (
+		parser.eat( `'` ) ? `'` :
+		parser.eat( `"` ) ? `"` :
+		null
+	);
+
+	const expressionStart = parser.index;
+
+	const expression = readExpression( parser, expressionStart, quoteMark );
+
+	if ( expression.type !== 'ObjectExpression' ) {
+		parser.error( `Expected object expression`, expressionStart );
+	}
+
+	return {
+		start,
+		end: parser.index,
+		type: 'Transition',
+		name,
+		intro: type === 'in' || type === 'transition',
+		outro: type === 'out' || type === 'transition',
+		expression
+	};
+}
\ No newline at end of file
diff --git a/src/parse/state/tag.js b/src/parse/state/tag.js
index 48e8cd197e..901b250833 100644
--- a/src/parse/state/tag.js
+++ b/src/parse/state/tag.js
@@ -1,7 +1,7 @@
 import readExpression from '../read/expression.js';
 import readScript from '../read/script.js';
 import readStyle from '../read/style.js';
-import { readEventHandlerDirective, readBindingDirective } from '../read/directives.js';
+import { readEventHandlerDirective, readBindingDirective, readTransitionDirective } from '../read/directives.js';
 import { trimStart, trimEnd } from '../../utils/trim.js';
 import { decodeCharacterReferences } from '../utils/html.js';
 import isVoidElementName from '../../utils/isVoidElementName.js';
@@ -253,6 +253,12 @@ function readAttribute ( parser, uniqueNames ) {
 		};
 	}
 
+	const match = /^(in|out|transition):/.exec( name );
+	if ( match ) {
+		parser.eat( '=', true );
+		return readTransitionDirective( parser, start, name.slice( match[0].length ), match[1] );
+	}
+
 	let value;
 
 	// :foo is shorthand for foo='{{foo}}'
diff --git a/test/parser/samples/transition-intro/input.html b/test/parser/samples/transition-intro/input.html
new file mode 100644
index 0000000000..db14cfcb2f
--- /dev/null
+++ b/test/parser/samples/transition-intro/input.html
@@ -0,0 +1 @@
+<div in:style='{opacity: 0}'>fades in</div>
\ No newline at end of file
diff --git a/test/parser/samples/transition-intro/output.json b/test/parser/samples/transition-intro/output.json
new file mode 100644
index 0000000000..3f73ef3ce1
--- /dev/null
+++ b/test/parser/samples/transition-intro/output.json
@@ -0,0 +1,65 @@
+{
+	"hash": 3160753914,
+	"html": {
+		"start": 0,
+		"end": 43,
+		"type": "Fragment",
+		"children": [
+			{
+				"start": 0,
+				"end": 43,
+				"type": "Element",
+				"name": "div",
+				"attributes": [
+					{
+						"start": 5,
+						"end": 28,
+						"type": "Transition",
+						"name": "style",
+						"intro": true,
+						"outro": false,
+						"expression": {
+								"start": 15,
+							"end": 27,
+							"type": "ObjectExpression",
+							"properties": [
+								{
+									"start": 16,
+									"end": 26,
+									"type": "Property",
+									"method": false,
+									"computed": false,
+									"shorthand": false,
+									"kind": "init",
+									"key": {
+										"type": "Identifier",
+										"start": 16,
+										"end": 23,
+										"name": "opacity"
+									},
+									"value": {
+										"start": 25,
+										"end": 26,
+										"type": "Literal",
+										"value": 0,
+										"raw": "0"
+									}
+								}
+							]
+						}
+					}
+				],
+				"children": [
+					{
+						"start": 29,
+						"end": 37,
+						"type": "Text",
+						"data": "fades in"
+					}
+				]
+			}
+		]
+	},
+	"css": null,
+	"js": null
+}
\ No newline at end of file