class_docstr: Vision transformer basic head.
  
  ::
  
                                    SequencePool
                                         ↓
                                      Dropout
                                         ↓
                                     Projection
                                         ↓
                                     Activation
  
  
  The builder can be found in `create_vit_basic_head`.
class_docstr_tok: ["Vision","transformer","basic","head",".",":",":","SequencePool","\u2193","Dropout","\u2193","Projection","\u2193","Activation","The","builder","can","be","found","in","`","create_vit_basic_head","`","."]
code: def forward(self, x: torch.Tensor) -> torch.Tensor:
      # Performs pooling.
      if self.sequence_pool is not None:
          x = self.sequence_pool(x)
  
      # Performs dropout.
      if self.dropout is not None:
          x = self.dropout(x)
      # Performs projection.
      if self.proj is not None:
          x = self.proj(x)
      # Performs activation.
      if self.activation is not None:
          x = self.activation(x)
      return x
  
imports: from typing import Callable, Tuple
  import torch
  import torch.nn
  from pytorchvideo.layers.utils import set_attributes
  from torchvision.ops import RoIAlign
label_desc: Use image node_id 2 for calling the VisionTransformerBasicHead obj's underlying member method code with example usage: obj.forward(x) and returns: x