pandoc/test/command/custom-attributes.html

Custom attributes should automatically have data- added
in HTML5:
```
% pandoc -t html5
[hello]{foo="bar"}
^D
<span data-foo="bar">hello</span>
```

but not in HTML4:
```
% pandoc -t html4
[hello]{foo="bar"}
^D
<span foo="bar">hello</span>
```
HTML writer: insert data- in front of unsupported attributes. Thus, a span with attribute 'foo' gets written to HTML5 with 'data-foo', so it is valid HTML5. HTML4 is not affected. This will allow us to use custom attributes in pandoc without producing invalid HTML. 2017-07-25 13:13:24 +02:00			`Custom attributes should automatically have data- added`
			`in HTML5:`
			```
			`% pandoc -t html5`
			`[hello]{foo="bar"}`
			`^D`
			`<span data-foo="bar">hello</span>`
			```

			`but not in HTML4:`
			```
			`% pandoc -t html4`
			`[hello]{foo="bar"}`
			`^D`
			`<span foo="bar">hello</span>`
			```