Better fix:

Per suggestion of @martindholmes, instead of trying to select the correct
descendant text node(s), just examine the string value of the entire eg
element as a whole. The string() function call is not technically necessary
(because matches() wants a string there, it would happen automagically),
but its use makes what we are doing explicit and obvious.

P5/p5odds.odd

@@ -184,8 +184,8 @@
             </desc>
             <constraint>
               <sch:rule context="tei:eg">
-                <sch:report test="matches( ./text()[last()], '&#x0A;\s*$')">trailing newline not allowed</sch:report>
-                <sch:report test="matches( ./text()[1],      '^\s*&#x0A;')">leading newline not allowed</sch:report>
+                <sch:report test="matches( string(.), '&#x0A;\s*$')">trailing newline not allowed</sch:report>
+                <sch:report test="matches( string(.), '^\s*&#x0A;')">leading newline not allowed</sch:report>
               </sch:rule>
             </constraint>
           </constraintSpec>