filtering: imp docs

internal/filtering/filter.go

@@ -504,7 +504,7 @@ func (d *DNSFilter) parseFilterLine(
 		return false, "", nil
 	}
 
-	singleHTMLCheck.Do(func() { err = checkNotHTML(line) })
+	singleHTMLCheck.Do(func() { err = checkNonHTML(line) })
 	if err != nil {
 		return false, "", err
 	}
@@ -521,12 +521,12 @@ func (d *DNSFilter) parseFilterLine(
 	return true, "", nil
 }
 
-// checkNotHTML detects if the line contains HTML tags.  line shouldn't have leading
-// space symbols.
+// checkNonHTML returns an error if the line contains HTML tags instead of plain
+// text.  line shouldn have no leading space symbols.
 //
 // TODO(ameshkov):  It actually gives too much false-positives.  Perhaps, just
 // check if trimmed string begins with angle bracket.
-func checkNotHTML(line string) (err error) {
+func checkNonHTML(line string) (err error) {
 	line = strings.ToLower(line)
 
 	if strings.HasPrefix(line, "<html") || strings.HasPrefix(line, "<!doctype") {