The default for x1, y1 and y2 is 0% for LinearGradient

Source/core/svg/SVGLinearGradientElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007 Rob Buis <buis@kde.org>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008 Dirk Schulze <krit@webkit.org>
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 19 matching lines @@
 
 namespace blink {
 
 inline SVGLinearGradientElement::SVGLinearGradientElement(Document& document)
     : SVGGradientElement(SVGNames::linearGradientTag, document)
     , m_x1(SVGAnimatedLength::create(this, SVGNames::x1Attr, SVGLength::create(SVGLengthMode::Width), AllowNegativeLengths))
     , m_y1(SVGAnimatedLength::create(this, SVGNames::y1Attr, SVGLength::create(SVGLengthMode::Height), AllowNegativeLengths))
     , m_x2(SVGAnimatedLength::create(this, SVGNames::x2Attr, SVGLength::create(SVGLengthMode::Width), AllowNegativeLengths))
     , m_y2(SVGAnimatedLength::create(this, SVGNames::y2Attr, SVGLength::create(SVGLengthMode::Height), AllowNegativeLengths))
 {
+
+    // Spec: If the x1|y1|y2 attribute is not specified, the effect is as if a value of "0%" were specified.
+    m_x1->setDefaultValueAsString("0%");
+    m_y1->setDefaultValueAsString("0%");
+    m_y2->setDefaultValueAsString("0%");
+
     // Spec: If the x2 attribute is not specified, the effect is as if a value of "100%" were specified.
     m_x2->setDefaultValueAsString("100%");
 
     addToPropertyMap(m_x1);
     addToPropertyMap(m_y1);
     addToPropertyMap(m_x2);
     addToPropertyMap(m_y2);
 }
 
 DEFINE_TRACE(SVGLinearGradientElement)
@@ skipping 114 matching lines @@
 
 bool SVGLinearGradientElement::selfHasRelativeLengths() const
 {
     return m_x1->currentValue()->isRelative()
         || m_y1->currentValue()->isRelative()
         || m_x2->currentValue()->isRelative()
         || m_y2->currentValue()->isRelative();
 }
 
 } // namespace blink