Whitespaces in attributes are not supported with the simplified XML input. The string below is an example of an XML definition that does not work during the import.

<a href = "http://www.example.com" target = "_blank"><b>Example</b></a>

After the simplified input transformation the result is:
<link href=""><strong>Example</strong></link>

Error: the href value is empty instead of containing the link value.

According to W3Cs XML specification of attributes:
Attribute ::= Name Eq AttValue
You can have zero or multiple spaces in the Eq part:
Eq ::= S? '=' S?

Steps to reproduce

Disable OE and paste in the following text:
<a href = "http://www.example.com" target = "_blank"><b>Example</b></a>
Click store draft and notice the result:
<link href=""><strong>Example</strong></link>