multiple pages: normalize regular expression instead of regex, regexp or pattern (#5830)

pages/common/sed.md

@@ -5,11 +5,11 @@
 
 - Replace the first occurrence of a regular expression in each line of a file, and print the result:
 
-`sed 's/{{regex}}/{{replace}}/' {{filename}}`
+`sed 's/{{regular_expression}}/{{replace}}/' {{filename}}`
 
 - Replace all occurrences of an extended regular expression in a file, and print the result:
 
-`sed -r 's/{{regex}}/{{replace}}/g' {{filename}}`
+`sed -r 's/{{regular_expression}}/{{replace}}/g' {{filename}}`
 
 - Replace all occurrences of a string in a file, overwriting the file (i.e. in-place):