If we create a custom field with field type Single-line Text Box or Multi-line Text Box.
The content of this field is free text, just like the content of Subject field.
When we create a Filter, for Subject field there is four option: contains, does not contain, is, is not
But, for a custom field with type is Single-line Text Box or Multi-line Text Box, we just have two options: is and is not.
Could we add the option: contains and does not contain when we make a filter using a custom field with type: single-line and multi-line text box.