For all callback related parameter like ShowIf, HideIf, EnableIf, DisableIf, RequiredIf, FieldShowIf, FieldHideIf, FieldEnableIf, FieldDisableIf, and the show parameter in InfoBox, AboveText etc.

They use this XPath-like syntax, but the start point is from the current field.

For example, by using upwalk, damage will only be enabled if it's a member (field/propery) of BuildObject type (or its subtype)

[Serializable]
public class BuildingAttackBrain
{
    [EnableIf("..@as(BuildObject)")]
    [InfoBox("Only available in BuildObject type", show: "..@not-as(BuildObject)")]
    public int damage;
}

you can also downwalk

[Serializable]
public struct DownWalkProp
{
    public string myContent;
}

// same as: [AboveText("<field.myContent/>")]
[AboveText("$field::" + nameof(DownWalkProp.myContent))]
public DownWalkProp v2;