diff --git a/surveys/unreadable-objects.md b/surveys/unreadable-objects.md
new file mode 100644
index 0000000..89a75d0
--- /dev/null
+++ b/surveys/unreadable-objects.md
@@ -0,0 +1,52 @@
+# Unreadable objects
+
+This is a survey of the lexical syntax that the `write` procedure uses
+to write unreadable objects.
+
+| Implementation | Syntax   | Skippable |
+|----------------|----------|-----------|
+| Chez Scheme    | `#<...>` | no        |
+| Chibi-Scheme   | `#<...>` | no        |
+| Chicken        | `#<...>` | no        |
+| Gambit         | `#<...>` | no        |
+| Gauche         | `#<...>` | no        |
+| Guile          | `#<...>` | no        |
+| Kawa           | `#<...>` | no        |
+| MIT Scheme     | `#[...]` | no        |
+| Mosh           | `#<...>` | no        |
+| Sagittarius    | `#<...>` | no        |
+| STklos         | `#[...]` | YES?      |
+| (Common Lisp)  | `#<...>` | no        |
+
+**Skippable** means that the written stand-in object can be parsed as
+an S-expression (using the syntax of that implementation) and
+therefore skipped to find more S-expressions in the same stream.
+
+## Conflicts
+
+Chicken and Gambit support multi-line strings via the following
+syntax. (The syntax imitates the Bourne shell, which calls a
+multi-line string a "here-document".)
+
+    <<end
+    .
+    .
+    .
+    end
+
+An arbitrary identifier can be used in place of `end`.
+
+SRFI 107 (_XML reader syntax_) uses `#<` for XML tags mixed in with
+Scheme code. It is implemented by Kawa. An example of this syntax is
+`#<da></da>`.
+
+In both cases there is a syntactic ambiguity. Chicken, Gambit, and
+Kawa all use `#<` to write unreadable objects. Since valid Scheme
+source code cannot contain unreadable objects, there is no read-time
+ambiguity for valid code. The ambiguity does make it harder to deal
+with invalid input where an unreadable object may be silently
+misinterpreted as some type of readable object or rejected with a
+confusing error message.
+
+STklos has a similar syntax `#<<end` but since it does not use
+`#<...>` for unreadable data there is no ambiguity.
diff --git a/www-index.scm b/www-index.scm
index d24cefc..92e87be 100644
--- a/www-index.scm
+++ b/www-index.scm
@@ -89,6 +89,7 @@
   "reader-vertical-bar-concatenated-with-number"
   "square-brackets"
   "string-symbol-conversion"
+  "unreadable-objects"
   "unsigned-imaginary"
   "upper-case-escape"
   "vertical-line-symbols")