问题
Could anyone clarify the difference between single and double quotation marks in HTML5 & CSS.
Here's Google's contradictory use of single quotes in HTML:
<link href='https://fonts.googleapis.com/css?family=Roboto' rel='stylesheet' type='text/css'>
And CSS:
font-family: 'Roboto', sans-serif;
While Bootstrap's documentation practices demonstrate the use of double quoted marks in HTML:
<link rel="stylesheet" href="https://cdn.rawgit.com/twbs/bootstrap/v4-dev/dist/css/bootstrap.css">
And CSS:
font-family:"Helvetica Neue",Helvetica,Arial,sans-serif;
Which practice is the best and why ?
EDIT: Is there any valid reason why Google Fonts decided to use single quotes ?
回答1:
Either are valid, but you probably should stick to a certain style guide. For example, Google's style guide suggest using double quotes for HTML and single quotes for CSS. (Although Google Fonts doesn't follow this exactly)
回答2:
There's no best practice, because neither has any affect at all on how the code is parsed. You can deliminate attributes and other strings using ' or " interchangeably.
回答3:
Generally, no difference. They are interchangeable.
The only important note is not to use one inside itself.
For example in php:
echo '"hello world"';
Outputs - "hello world"
Or
echo "'hello world'";
Outputs 'hello world'
BUT
echo ""hello world"";
Will throw an error if the " is unescaped, as it's closing that parameter before the contents.
来源：https://stackoverflow.com/questions/33697934/single-versus-double-quotation-marks-in-html-css