Template:Infobox/doc

Test Infobox
Label 1	Data 1
Label 2	Data 2
Label 3	Data 3
Header 4
Label 5	Data 5: Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
	Below text

{{Infobox
|name    = {{subst:PAGENAME}}
|title   = Example of an optional header
|header1 = {{#if:{{{item_one|}}}{{{item_two|}}}{{{item_three|}}}|Optional header}}
|label2  = Item one
|data2   = {{{item_one|}}}
|label3  = Item two
|data3   = {{{item_two|}}}
|label4  = Item three
|data4   = {{{item_three|}}}
}}

header1 will be shown if any of item_one, item_two, or item_three is defined. If none of the three parameters are defined the header won't be shown.

The trick to this is that the "if" returns false only if there is nothing whatsoever in the conditional section, so only if all three of item_one, item_two and item_three are undefined will the if statement fail.