Also accept s HTML tags.

doc/snac.5

@@ -59,7 +59,7 @@ converted to related emojis:
 All HTML tags in entries are neutered except the following ones:
 .Bd -literal
 a p br blockquote ul ol li cite small
-span i b u pre code em strong hr img del
+span i b u s pre code em strong hr img del
 .Ed
 .Pp
 .Ss Disk Layout

format.c

@@ -203,7 +203,7 @@ xs_str *not_really_markdown(const char *content, xs_list **attach)
 
 const char *valid_tags[] = {
     "a", "p", "br", "br/", "blockquote", "ul", "ol", "li", "cite", "small",
-    "span", "i", "b", "u", "pre", "code", "em", "strong", "hr", "img", "del", NULL
+    "span", "i", "b", "u", "s", "pre", "code", "em", "strong", "hr", "img", "del", NULL
 };
 
 xs_str *sanitize(const char *content)