Hi,

how can I create different extra fields for different units? E.g. in WH40k I have infantry with the extra field "ballistic skill", "strength", "toughness" and so on. And there are tanks which lack these fields but have other ones like "front armour", "rear armour" and so on.

You can define all of those extra fields and then leave "front armour" blank for infantry units etc.
Then You can use custom display script(I will be glad to help You with this) to define how to display different types of units on pdf.

Please,
I'd be interested to see an example of this as I have some vehicle in my ruleset thast have different stats than infantry.

OK
You can see Infinity Rulesets for example
[armycalc.com]
'Flesh' units in this game have Wounds and 'non-flesh' units have Strength.
Extra fields defines both W and STR with "-" as a default value

    <field>
      <name>W</name>
      <default>-</default>
    </field> 
    <field>
      <name>STR</name>
      <default>-</default>
    </field>

Then some of the units have defined W and some STR with the other one undefined:

<field><name>W</name><value>1</value></field>

or

<field><name>STR</name><value>1</value></field>

And then on army lists you get the same results as in Warhammer army books. Undefined fields are marked as '-'

If this is 'messy' you can try to write custom display script that will not print fields with value '-' at all. I can take a look at your ruleset and help with this if you like.

I would prefer the display script solution for sure if it does the following:
- Works on both online and offline versions.
- Affects both the displayed and printed output.

You can freely check on my rulesets -
let's say: Warzone 2nd- Cybertronic
"Eradicator Deathdroid" is a vehicle and has a different stat than units.

Once again, thanks for your help, much appreciated-

Unfortunatelly custom displays are not well tested in both online and offline editors.
That's because no ruleset is using them.

Unfortunately this will not affect displayed output. the concept is that there is a one set of displayed fields. this way army can be displayed as a table.
Note that in online editor the driver is displayed in the same table as Eradicator Deathdroid.

I took a look at your ruleset and can see any fields defined in Eredicator not defined elsewhere. How many of such fields will be there?
If just a few then the best solution in my opinion is what I did on your ruleset:
In edit ruleset view added 'X' file with default '-' for display fields.
Define this field for Eredicator but not define it anywhere else.

Check how it looks like and if it fits you.

I have the same issue with my Ruleset: Black Templar 4th edition WH40k including FAQ 1.1

It is a Warhammer 40k ruleset where units on foot and vehicles have different stats.

I am currently entering the different stats, so there's not that much to look so far at except for the Dreadnaught.

Is there any documentation/tutorial on creating a display script?

Here it is:
[armycalc.com]
But unfortunately no ruleset had really used this functionality and all of them are using the default display (for example in online editor you do not even have an option to select other display script than default).
I advise you to wait for twr 3.0 for a customisation like that. sorry

No problem, I'll wait.