diff --git a/spec.md b/spec.md
index 5f40029..e6d5a23 100644
--- a/spec.md
+++ b/spec.md
@@ -82,6 +82,8 @@ subject.cid   -- "bafyreicuxyp5rmsrqsf3v63ww6gc3j7q6cp7qyk6bv47c3bqkj2gzswiqq"
 
 Object field names can be arbitrary strings, so RecordPath needs to disambiguate its own syntax when fields contain syntax characters.
 
+The backslash is the conventional escape character in many languages and systems, but as per the URL-unreserved character constraint in section 1, it cannot be used here. The exclamation mark ! serves as its replacement.
+
 RecordPath has six syntax characters, which must be escaped by a preceeding `!` if they appear in a field name in the path.
 
 | Literal | Escaped | Syntax hint       |