String
This is a user-given string, which is typically used for referencing another command.
ELEMENT_BOUNDARY_CONDITION( "inflow" ) {
element_set = "channel"
}
element_set references the element set "channel" given above. The quotes surrounding a string may be omitted if the string contains only alphanumeric and underscore characters. However, strings that are not quoted are automatically converted to lower case and thus this practice is not recommended.