2.1.10 [CSS-Level2-2009] Section 5.7, Adjacent sibling selectors
The specification states:
Adjacent sibling selectors have the following syntax: E1 + E2, where E2 is the subject of the selector. The selector matches if E1 and E2 share the same parent in the document tree and E1 immediately precedes E2, ignoring non-element nodes (such as text nodes and comments).
Quirks Mode (All Versions)
The adjacent sibling selector is not supported; therefore, styling based on this selector is not supported.
IE7 Mode (All Versions)
Comments are not ignored for adjacent sibling selectors.