Is a tabulator a valid character for whitespace between elements in XML/SOAP?
<a>*TAB*
*TAB*<b>test</b>*TAB*
</a>
*TAB* stands for \t = 0x09
Based on specification 0x09 is allowed in XML/SOAP.
Section 2.2 is about characters and as you can see is allowing you to use:
from characters before 0x20.
Yes, tab characters (CHARACTER TABULATION: 	
or 	
) are allowed in XML content (but not in XML names):
Char ::= #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]