diff --git a/ch02.adoc b/ch02.adoc
index d024706c..1c5a2e2e 100644
--- a/ch02.adoc
+++ b/ch02.adoc
@@ -51,6 +51,7 @@ By the word _letters_ we mean the standard ASCII letters uppercase `A` to `Z` an
 By the word _digits_ we mean the standard ASCII digits `0` to `9`, and similarly _underscores_ means the standard ASCII underscore `_`.
 Note that this is in conformance with the COARDS conventions, but is more restrictive than the netCDF interface which allows almost all Unicode characters encoded as multibyte UTF-8 characters (link:$$https://docs.unidata.ucar.edu/nug/current/file_format_specifications.html$$[NUG Appendix B]).
 The netCDF interface also allows leading underscores in names, but the NUG states that this is reserved for system use.
+ASCII period (.) and ASCII hyphen (-) are also allowed in attribute names only.
 
 Case is significant in netCDF names, but it is recommended that names should not be distinguished purely by case, i.e., if case is disregarded, no two names should be the same.
 It is also recommended that names should be obviously meaningful, if possible, as this renders the file more effectively self-describing.
diff --git a/conformance.adoc b/conformance.adoc
index 1cb3d546..99f4435c 100644
--- a/conformance.adoc
+++ b/conformance.adoc
@@ -37,6 +37,7 @@ See https://github.com/ugrid-conventions/ugrid-conventions for the UGRID conform
 *Recommendations:*
 
 * Variable, dimension and attribute names should begin with a letter and be composed of letters (A-Z, a-z), digits (0-9), and underscores(_). This corresponds to ASCII characters in the decimal ranges (65-90), (97-122), (48-57), and (95). The corresponding Unicode codepoints are (U+0041-U+005A), (U+0061-U+007A), (U+0030-U+0039), and (U+005F).  
+* ASCII period (.) and ASCII hyphen (-) may also be included in attribute names only.
 * No two variable names should be identical when case is ignored.
 
 [[section-2]]
diff --git a/history.adoc b/history.adoc
index 39745b95..93a99824 100644
--- a/history.adoc
+++ b/history.adoc
@@ -7,6 +7,7 @@
 
 === Working version (most recent first)
 
+* {issues}477[Issue #477]: Period and hyphen allowed in attribute names
 * {issues}500[Issue #500]: Appendix B: Added a **`conventions`** string to the standard name xml file format definition
 
 === Version 1.11 (05 December 2023)