In Baray's synergy effect "+4 industy for each neighbouring river" it wrote "District.Nieghbours-(validation)Neighbours"

When I create a new legacy effect "+1 industy  on tiles for each neighbouring river" I thought I should write "MajorEmpire.Cities.District.Nieghbours-(validation)Neighbours" 

but it actually works as "+1 industy  on rivers". Otherwise when I write "MajorEmpire.Cities.District.Nieghbours-(validation)-Districts"

it works as "+1industy  on tiles for each neighbouring river"(like Baray's synergy effect) instead.

Does the "path" works in totally different ways when it uses different "source"?

In the first picture: The "source" is the district where this descriptor is applied to (in this case the baray district). The Target is the last entry in the path. Since neighbors of districts are also districts (please note, any tile on the playfield is considered a "district"). The baray normally adds its neighbor bonus unto itself. You can change it to target, and the bonus will be applied to its neighbors which are river tiles instead.

What you could do is using an event which fires when you build an extension. Make it check the specific district type (or give it a special tag) and then you can apply a synergy descriptor to the freshly built district.

sad part: you cannot "see" this in the LT overview ingame. Maybe with some tricking you can do it, but not with normal stuff not. 

What you could try:

- make a new district tag 

- add this tag to the district

- add this tag as validator in the LT effect for districts. The effect you want (like  add 2 industry). Path should be Only: EmpireMajor.Cities:Districts

- make a validationmapper for that new tag: As localisation you write something "Makers Districts which neighbors to river tiles." You can use some stuff like [MoneyColored] in this text field. You may have to try this 1 or 2 times to get the text right. Look at the following link for the vanilla texts and how they are done: Link (not by me, is somewhere here in the forums though)

- make a SECOND effect with the same as above, but instead subtract it

- now make an effectmapper for that descriptor where the effects come from

-- add one effect policy, insert the correct effect index and property effect index of the second effect which subtracts the effect again and make that hidden for the subtraction (all start with 0 as the very first entry). 

Effect Index = the whole effect with its path, its validator and the property effect. The first in the list is 0

Property Effect Index = the Property Effect of an effect. The first on in the list is 0 and for each effect separate

- add the event which does what you actually want. You can look at my event guide in the modding sub. The last example of the first post explains something very similar.

I have not tested this, but it should work.