2.2.16 [W3C-XSLT] Section 16.2, HTML Output Method

C0021:

The specification states:

 The html output method may output a character using a character entity reference, if
 one is defined for it in the version of HTML that the output method is using.

MSXML3 and MSXML6

The html output method writes a character using a character entity reference, if one is defined for it in the version of HTML that the output method is using.