====== DED syntax ======

This page describes the common syntax elements of the [[ded]] (Doomsday Engine Definition) language.

===== Directives =====

Directives instruct the DED [[http://en.wikipedia.org/w/index.php?title=Parser|parser]] to perform special actions when encountered.

^ Keyword^ Description |
| [[include|Include]]| Include the specified //.DED// file. |
| [[include|IncludeIf]]| Include the specified //.DED// file if the conditional statement is **true**. |
| [[skip|SkipIf]]| Skip the rest of the current file if the conditional statement is **true**. |
| [[model_path|ModelPath]]| Append a new path to the list of model search paths. |



===== Comments =====

There are two kinds of comment in DED; single-line and multi-line.

Single line comments begin with **#** and continue until the end of line.

<code># A single line comment stops here
</code>
Multi line comments begin with **#>** and continue until **<#** is found.
  
  #> A multi-line comment begins...
  And continues
  ...and ends here <#


===== Assignment statements =====


==== Flag values ====

<code>Property = flaga | flagb | flagc;  # Version 6 syntax
Property = "flaga flagb flagc";    # Version 5 syntax (still supported).
</code>
The special case of 'no flags' is defined as follows:
  
  Property = 0;   # Supported from Doomsday 1.9.9 onwards
  Property = "";  # Version 5 syntax

<note warning>
The following is a syntax error:
  Property = ;
</note>


==== String values ====

Strings begin and end with **"** (double quotation mark). If newline (''\n'') characters are found inside a string (the string has been divided into multiple lines) the newline and all following whitespace are skipped, and the actual string continues from the first non-whitespace character that follows.

  Property = "Some text string";

To include a double quotation mark in the string itself, [[http://en.wikipedia.org/wiki/Escape_sequence|escape]] it with **\** (backward slash).

  Property = "Some \"quoted text\"";

To include a backward slash in the string itself, it must appear twice (to escape the escape sequence).

<code>Property = "path\\to\\something";
</code>

For this reason it is generally better to use forward slashes in paths. Doomsday uses forward slashes on all platforms, internally.


==== URI values ====

Resource [[uri]]s are used throughout Doomsday and use the following form:
  Property = "<scheme>:<path>";


===== Definition scopes =====

A scope describes the extent of zero or more definition statements which apply to a named [[ded#Definition_types|definition type]].

Syntax example:
  <attribute> definitiontype <attribute> <identifier> {
    //... Definition statements ...//
  }


==== Attributes ====

Attributes are optional keywords that either precede or follow a scope. These "derivation" attributes change the behavior of the parser when interpreting definition statements within the scope.

^ Keyword ^ Description |
| [[altering_and_copying_definitions|Copy]]| Use the previous definition of the same type as a base. |
| [[altering_and_copying_definitions|Mods]]| Modify an existing definition. |

Clever use of attributes in conjunction with [[#Directives|directives]] allows the add-on author to construct multi-part, combinatorial add-ons.


===== Example =====

The following snippet (taken from //libdoom.pk3:defs/doom1/materials.ded//) serves as good example of what a //.DED// file typically looks like:
  
  Header { Version = 6; }
  
  # Allow disabling from the command line.
  SkipIf -nodefaultfx;
  
  # Add an animated light glow effect to the NUKAGE1 material.
  Material Mods "flats:NUKAGE1" {
    Layer {
        Stage { Glow = .5;  Tics = 24; Rnd = .5; }
        Stage { Glow = .44; Tics = 24; Rnd = .5; }
    }
  }



===== See also =====

  *  [[:ded|DED language overview]]
  *  [[Flags reference]]