See https://www.zabbix.com/documentation/4.0/manual/config/items/itemtypes/zabbix_agent .
Many item keys support regexp in parameters, but the detail about that regexp is inconsistent and sometimes a bit lacking.

For example, several different ways of saying this is regexp are used:

• "regular expression describing the required pattern"
• "regex describing the file, directory and symbolic link name"
• "Perl Compatible Regular Expression (PCRE) or POSIX extended regular expression before Zabbix 3.4"

Along with the inconsistencies above, system.hw.macaddr and system.sw.packages do not say which regexp flavour is it.

It is suggested to reduce all mentions to "regular expression" (while leaving the functional description intact), and having a footnote which explains the details. For example, the entries above could be changed to:

• "regular expression[4] describing the required pattern"
• "regular expression[4] describing the file, directory and symbolic link name"
• "regular expression[4]"

The footnote would be:

[4] Perl Compatible Regular Expression (PCRE) or POSIX extended regular expression before Zabbix 3.4.

While at this, one might want to change the exception occurrences of "regex" in vfs.dir.count and vfs.dir.size to "regexp", to be consistent.