正如我在评论中所说，HTMLParser 将其添加为 CSS 属性，
正如 Jasper 已经回答的那样，它是由规范决定的。
实施
Webkit 解析 HTMLParser.cpp 中的 html，如果 Parser 是 inBody，它会将 bgColor 属性添加为 HTMLBodyElement.cpp 中的 CssColor
// Color parsing that matches HTML's "rules for parsing a legacy color value"
void HTMLElement::addHTMLColorToStyle(StylePropertySet* style, CSSPropertyID propertyID, const String& attributeValue)
{
// An empty string doesn't apply a color. (One containing only whitespace does, which is why this check occurs before stripping.)
if (attributeValue.isEmpty())
return;
String colorString = attributeValue.stripWhiteSpace();
// "transparent" doesn't apply a color either.
if (equalIgnoringCase(colorString, "transparent"))
return;
// If the string is a named CSS color or a 3/6-digit hex color, use that.
Color parsedColor(colorString);
if (!parsedColor.isValid())
parsedColor.setRGB(parseColorStringWithCrazyLegacyRules(colorString));
style->setProperty(propertyID, cssValuePool().createColorValue(parsedColor.rgb()));
}
你很有可能以这种方法结束：
static RGBA32 parseColorStringWithCrazyLegacyRules(const String& colorString)
我认为是支持这样的旧颜色：body bgcolor=ff0000 (Mozilla Gecko Test)。
- 跳过前导#
- 获取前 128 个字符，将非十六进制字符替换为 0。
第1120章
- 非 BMP 字符被替换为“00”，因为它们在字符串中显示为两个“字符”。
- 如果没有数字返回颜色黑色
- 将数字分成三个部分，然后搜索每个部分的最后 8 位。
Webkit/HTMLElement.cpp:parseColorStringWithCrazyLegacyRules的代码：
static RGBA32 parseColorStringWithCrazyLegacyRules(const String& colorString)
{
// Per spec, only look at the first 128 digits of the string.
const size_t maxColorLength = 128;
// We'll pad the buffer with two extra 0s later, so reserve two more than the max.
Vector<char, maxColorLength+2> digitBuffer;
size_t i = 0;
// Skip a leading #.
if (colorString[0] == '#')
i = 1;
// Grab the first 128 characters, replacing non-hex characters with 0.
// Non-BMP characters are replaced with "00" due to them appearing as two "characters" in the String.
for (; i < colorString.length() && digitBuffer.size() < maxColorLength; i++) {
if (!isASCIIHexDigit(colorString[i]))
digitBuffer.append('0');
else
digitBuffer.append(colorString[i]);
}
if (!digitBuffer.size())
return Color::black;
// Pad the buffer out to at least the next multiple of three in size.
digitBuffer.append('0');
digitBuffer.append('0');
if (digitBuffer.size() < 6)
return makeRGB(toASCIIHexValue(digitBuffer[0]), toASCIIHexValue(digitBuffer[1]), toASCIIHexValue(digitBuffer[2]));
// Split the digits into three components, then search the last 8 digits of each component.
ASSERT(digitBuffer.size() >= 6);
size_t componentLength = digitBuffer.size() / 3;
size_t componentSearchWindowLength = min<size_t>(componentLength, 8);
size_t redIndex = componentLength - componentSearchWindowLength;
size_t greenIndex = componentLength * 2 - componentSearchWindowLength;
size_t blueIndex = componentLength * 3 - componentSearchWindowLength;
// Skip digits until one of them is non-zero,
// or we've only got two digits left in the component.
while (digitBuffer[redIndex] == '0' && digitBuffer[greenIndex] == '0'
&& digitBuffer[blueIndex] == '0' && (componentLength - redIndex) > 2) {
redIndex++;
greenIndex++;
blueIndex++;
}
ASSERT(redIndex + 1 < componentLength);
ASSERT(greenIndex >= componentLength);
ASSERT(greenIndex + 1 < componentLength * 2);
ASSERT(blueIndex >= componentLength * 2);
ASSERT(blueIndex + 1 < digitBuffer.size());
int redValue = toASCIIHexValue(digitBuffer[redIndex], digitBuffer[redIndex + 1]);
int greenValue = toASCIIHexValue(digitBuffer[greenIndex], digitBuffer[greenIndex + 1]);
int blueValue = toASCIIHexValue(digitBuffer[blueIndex], digitBuffer[blueIndex + 1]);
return makeRGB(redValue, greenValue, blueValue);
}