Question: Do we have a rule to use "PostgreSQL" and "<productname>PostgreSQL</productname>" separately?

Dear hackers,

While checking documentations, I found that one line notes our product as
"PostgreSQL", whereas another line notes as just
"PostgreSQL". For example, in bgworker.sgml:

```
PostgreSQL can be extended to run user-supplied code in separate processes.
...
These processes are attached to PostgreSQL's
shared memory area and have the option to connect to databases internally; ...
```

It seems that  tag is not used when the string is used as link or
title, but I cannot find other rule to use them. Could you please tell me discussions
or wikipage about it?

Best Regards,
Hayato Kuroda
FUJITSU LIMITED