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The tsvector data type has always forbidden lexemes to be empty. However, array_to_tsvector() didn't get that memo, and would allow an empty-string array element to become an empty lexeme. This could result in dump/restore failures later, not to mention whatever semantic issues might be behind the original prohibition. However, other functions that take a plain text input directly as a lexeme value do not need a similar restriction, because they only match the string against existing tsvector entries. In particular it'd be a bad idea to make ts_delete() reject empty strings, since that is the most convenient way to clean up any bad data that might have gotten into a tsvector column via this bug. Reflecting on that, let's also remove the prohibition against NULL array elements in tsvector_delete_arr and tsvector_setweight_by_filter. It seems more consistent to ignore them, as an empty-string element would be ignored. There's a case for back-patching this, since it's clearly a bug fix. On balance though, it doesn't seem like something to change in a minor release. Jean-Christophe Arnu Discussion: https://postgr.es/m/CAHZmTm1YVndPgUVRoag2WL0w900XcoiivDDj-gTTYBsG25c65A@mail.gmail.com
<!-- doc/src/sgml/README.links -->
Linking within DocBook 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
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
<link>
use to supply text for the link, only uses linkend, requires </link>
http://www.oasis-open.org/docbook/documentation/reference/html/link.html
can be embedded inside of <command>, unlike <xref>
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
----------
- For an internal link, if you want to supply text, use <link>, else
<xref>.
- Specific nouns like GUC variables, SQL commands, and contrib modules
usually have xreflabels.
- For an external link, use <ulink>, with or without link text.
- xreflabels added to tags prevent the chapter/section for id's from being
referenced; only the xreflabel is accessible. Therefore, use xreflabels
only when linking is common, and chapter/section information is unneeded.