Hey WebKittens! WebCore::Element has two functions covering with most of your attribute retrieval use cases:
const AtomicString& getAttribute(const QualifiedName&) const; bool hasAttribute(const QualifiedName&) const; An optimization was introduced in <http://trac.webkit.org/changeset/59281> to allow faster lookup of certain attributes. It bypasses resolution of the “style” attribute, and doesn’t update animatable SVG attributes before returning them. This makes it slightly faster (and perfectly safe) to use fastGetAttribute() and fastHasAttribute() for anything that isn’t HTMLNames::styleAttr or one of the SVG animatable attributes. The functions are documented in Element.h as follows: // Call this to get the value of an attribute that is known not to be the style // attribute or one of the SVG animatable attributes. Unfortunately since the introduction of the fast attribute functions, there has been some confusion about when and where it’s actually safe to use them. In fact, I discovered quite a few bugs when taking a closer look at this. Here is the full list of SVG animatable attributes in WebKit at the time of writing: In the HTMLNames namespace: class In the XLinkNames namepace: href In the SVGNames namespace: amplitude, azimuth, baseFrequency, bias, clipPathUnits, cx, cy diffuseConstant, divisor, dx, dy edgeMode, elevation, exponent, externalResourcesRequired filterRes, filterUnits, fx, fy gradientTransform, gradientUnits, height, in2 in, intercept, k1, k2 k3, k4, kernelMatrix, kernelUnitLength lengthAdjust, limitingConeAngle, markerHeight, markerUnits markerWidth, maskContentUnits, maskUnits, method mode, numOctaves, offset, operator order, orient, pathLength, patternContentUnits patternTransform, patternUnits, pointsAtX, pointsAtY pointsAtZ, preserveAlpha, preserveAspectRatio, primitiveUnits radius, r, refX, refY result, rotate, rx, ry scale, seed slope, spacing specularConstant, specularExponent spreadMethod, startOffset stdDeviation, stitchTiles surfaceScale, tableValues target, targetX targetY, transform type, values viewBox, width x1, x2 x xChannelSelector, y1 y2, y yChannelSelector, z The worst thing is that there’s been nothing stopping you from asking the fast functions about these attributes, you’ll simply get incorrect results in some cases. To get us out of this mess, I’ve added a assertions to verify that we aren’t micro-optimizing ourselves in the foot. The fast lookup functions now assert that fastAttributeLookupAllowed() is true for the requested attribute. For non-SVG elements, it simply checks that you aren’t asking for the “style” attribute. For SVG elements, it calls out to SVGElement::isAnimatableAttribute(). Oh, and these changes landed in <http://trac.webkit.org/changeset/97670>. Thanks for reading, and happy hacking! :) -Kling
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