Steps to reproduce:

1. Click Create Item
2. Choose type Zabbig agent
3. Click Select Key
4. Find web.page.regexp[host,<path>,<port>,<regexp>,<length>,<output>]

Result:
"regexp" parameter is wrongly documented it is marked as optional, but is mandatory.

Expected:
web.page.regexp[host,<path>,<port>,regexp,<length>,<output>]