/// <summary>Builds an AST that checks if a backreference has been matched.</summary>
/// <param name="source">The original backreference.</param>
internal BackEmptyAST(BackRefAST source)
: base()
{
Source = source;
}
/// <summary>Builds an AST that scans one character for a backreference.</summary>
/// <param name="source">The original backreference.</param>
internal BackCheckAST(BackRefAST source)
: base()
{
Source = source;
}
/// <summary>Builds an AST that checks if a backreference has been matched.</summary>
/// <param name="source">The original backreference.</param>
internal BackDoneAST(BackRefAST source)
: base()
{
Source = source;
}