The default argument, if given, has to be of exactly the same datatype
as the first argument; but this was not stated in so many words, and
the error message you get about it might not lead your thought in the
right direction. Per bug #13587 from Robert McGehee.
A quick scan says that these are the only two built-in functions with two
anyelement arguments and no other polymorphic arguments. There are plenty
of cases of, eg, anyarray and anyelement, but those seem less likely to
confuse. For instance this doesn't seem terribly hard to figure out:
"function array_remove(integer[], numeric) does not exist". So I've
contented myself with fixing these two cases.
<!-- doc/src/sgml/README.links -->
Linking within SGML documents can be confusing, so here is a summary:
Intra-document Linking
----------------------
<xref>
use to get chapter/section number from the title of the target
link, or xreflabel if defined at the target, or refentrytitle if target
is a refentry; has no close tag
http://www.oasis-open.org/docbook/documentation/reference/html/xref.html
<link>
use to supply text for the link, requires </link>
http://www.oasis-open.org/docbook/documentation/reference/html/link.html
linkend=
controls the target of the link/xref, required
endterm=
for <xref>, allows the text of the link/xref to be taken from a
different link target title
External Linking
----------------
<ulink>
like <link>, but uses a URL (not a document target); requires
</ulink>; if no text is specified, the URL appears as the link
text
http://www.oasis-open.org/docbook/documentation/reference/html/ulink.html
url=
used by <ulink> to specify the URL, required
Guidelines
----------
o If you want to supply text, use <link>, else <xref>
o Do not use text with <ulink> so the URL appears in printed output
o Specific nouns like GUC variables, SQL commands, and contrib modules
usually have xreflabels