Expanded Syntax : 
${macro-type(macro)}
 
Shorthand notation:
${macro}
 
Example Usage: 
${runtime(hostname)) - get hostname from runtime arguments
${token(hostname)) - get hostname from workflow token
${secure(access_key)) - get access key from secure store 
${function_time(time_format)) - apply time function on the time_format provided and use the value. 
 
The Default (short-hand) usage will read from runtime arguments, having an expanded notation gives user option for using more macro types.
Examples :
ipConfig : ${hostname}:${port}
JDBC connection string : jdbc:{jdbc-plugin}://{hostname}:{sql-port}/{db-name}
 

"stages": [
    {
        "name": "Database",
        "plugin": {
            "name": "Database",
            "type": "batchsource",
            "properties": {
				...
                "user": "${username}",
                "password": "${secure(sql-password)}",
                "jdbcPluginName": "jdbc",
                "jdbcPluginType": "${jdbc-type}",
                "connectionString": "jdbc:${jdbc-type}//${hostname}:${port}/${db-name}",
                "importQuery": "select * from ${table-name};"
            }
        }
    },
    {
        "name": "Table",
        "plugin": {
            "name": "Table",
            "type": "batchsink",                                        
            "properties": {
                "schema": "{\"type\":\"record\",\"name\":\"etlSchemaBody\",
                \"fields\":[{\"name\":\"name\",\"type\":\"string\"},
                {\"name\":\"age\",\"type\":\"int\"},{\"name\":\"emp_id\",\"type\":\"long\"}]}",
                "name": "${table-name}",
                "schema.row.field": "name"
            }
        }
    }
]

interface MacroContext {	
	/**
	 * Given the macro key, return the translated value
     */ 
	String getValue(String macroKey);
}

Based on the macro type, one of the below MacroContext's will be used to get the value for macro. 
 
DefaultMacroContext implements MacroContext {
	Map<String, String> runtimeArguments;
	String getValue(String macroKey) {
		return runtimeArguments.get(macroKey);
	}
}

SecureMacroContext implements MacroContext {
	SecureStore secureStore;
	String getValue(String macroKey) {
		return secureStore.get(macroKey);
	}
}

RuntimeFunctionMacro implements MacroContext {	
	TimeZone timeZone;
	long logicalStartTime;
	Function<String, String> timezoneFunction;
	String getValue(String arguments) {
		return timezoneFunction.apply(arguments);
	}
} 
 

// if a pipeline config fields does not support macro, can be specified at config level. 
// if not specified by default, all fields can be macro substituted
@Macro(enabled=false) 
public static class ValidatorConfig extends PluginConfig {
  @Description("Comma-separated list of validator plugins that are used in script")
  String validators;
  @Description(SCRIPT_DESCRIPTION)
  String validationScript;

  @Description("Lookup tables to use during transform. Currently supports KeyValueTable.")
  @Nullable
  String lookup;
}

public class TableSinkConfig extends PluginConfig {
  @Name(Properties.Table.NAME)
  @Description("Name of the table. If the table does not already exist, one will be created.")
  private String name;

  @Name(Properties.Table.PROPERTY_SCHEMA)
  @Description("schema of the table as a JSON Object. If the table does not already exist, one will be " +
    "created with this schema, which will allow the table to be explored through Hive. If no schema is given, the " +
    "table created will not be explorable.")
  @Nullable
  @Macro(enabled=false)	
  // schema cannot be macro substituted, other fields can be macro substituted.
  private String schemaStr;

  @Name(Properties.Table.PROPERTY_SCHEMA_ROW_FIELD)
  @Description("The name of the record field that should be used as the row key when writing to the table.")
  private String rowField;
}

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Macro {

  /**
   * Default status if macro is enabled.
   */
  boolean DEFAULT_STATUS = true;

  /**
   * Returns if macro is enabled. Default is 'true'.
   */
  boolean enabled() default DEFAULT_STATUS;
}
 

/**
 * Contains information about a property used by a plugin.
 */
@Beta
public class PluginPropertyField {

  private final String name;
  private final String description;
  private final String type;
  private final boolean required;
  // returns true if this field can accept macro
  private final boolean macroEnabled;
  ...
}