This document describes the syntax of expressions used inside of YAML to perform lookups, selections or calculations.

Typically this is found after $where ($where: item.Amount is 0), inside of collection key expressions (surrounded by parentheses, (item.Amount is 0):), after numeric members Amount: 32 * Scale, or in explicit expression members ($Description: SharedDescription concat "\nThis one is for Humans.")

true and false

Normal base 10 decimal rules.

Example: 10, 12.34e+5

/[-+]?[0-9]*\.?[0-9]+(?:e[-+]?[0-9]+)/

Normal string rules, double quotes.

Example: "Example.", "New\nlines\n"

/(?<![""\\])""(?:[^""\\]|\\.)*?""(?!=[""\\])/

These are the same escape sequences as C#.

In the context of a definition, refers to the definition object. So for example, in a Government: context, any fields on the Government definition type are valid members.

• The ID of the government, def.GovernmentId
• The government's name, def.Name
• The government's first bonus' type, def.Bonuses[0].Type

Otherwise this symbol's name should be reserved.

In the context of a collection, refers to the collection itself.

So for example, in a Government: ... Bonuses: collection context, you have access to the collection itself.

• The government's first bonus, collection[0]
• The type of the first bonus, collection[0].Type

Otherwise this symbol's name should be reserved.

In the context of a collection, refers to the collection item.

In the context of a selection expression, (e.g. list item selection, e.g. (...)) refers to the current item.

So for example, in a Government: ... Bonuses: collection context, any fields on the Bonus type are valid members.

• The type of the bonus, item.Type

Otherwise this symbol's name should be reserved.

In the context of a field member, refers to the previous value.

In the context of a selection expression, (e.g. list item selection, e.g. (...)) refers to the current value.

For example, when you're updating a value using an update or update-all instruction,

• To get the previous value, you can just refer to value
• To replace some text in a previous Description: field, you can express it as,
  $Description: value replace "Technocracy government type is only available to the Ackdarian race." with "All your base are belong to us."

Otherwise this symbol's name should be reserved.

In the context of an empire specific definition (like EmpirePolicy), refers to the Empire object.

Currently this is only applicable to the EmpirePolicy: context.

Since this definition type can apply to multiple empires, you may want to express different possibilities.

This should always be of a Empire type object while in the context of an empire specific type.

Otherwise this symbol's name should be reserved.

This refers to the DWGame object. You can use this to get and compare the Game's version.

Example: v(game.Version) in versions "(,1.1)"

This refers to the Galaxy object.

Generally this is only available in the context of a running game, such as during empire creation and updating of EmpirePolicy.

Otherwise this symbol's name should be reserved.

This refers to the ModManager object. You can use this to get and compare the Mod Loader's version.

Example: loader.Version in versions "[1.2,)"

You may theoretically also use this to check for the existence of other mods. (Needs to be documented.)

. is used to resolve member fields and properties.

Example: A.B will resolve the B member of A.

[expression] where expression can be a number or full expression, performs an index resolution operation as necessary to access a collection member. The majority of indexes are zero based, it is probably safe to assume all of them are. This may be referred to as a subexpression or nested expression.

Example: A[11] (or A[8+3], etc.) will resolve index 11 in the collection of A. If A is a string, this will return the 12 character, otherwise it may return the 12th item.