Below is a list of Knack's field types along with your options for the operator value for each.

Field Type	Filters Permitted
Short Text	contains, does not contain, is, is not, starts with, ends with, is blank, is not blank
Paragraph Text	contains, does not contain, is, is not, starts with, ends with, is blank, is not blank
Yes/No	is, is not, is blank, is not blank
Multiple Choice	is, is not, contains, does not contain, is any, is blank, is not blank
Date/Time (single date)	is, is not, is during the current, is during the previous, is during the next, is before the previous, is after the next, is before, is after, is today, is today or before, is today or after, is before today, is after today, is before current time, is after current time, is blank, is not blank
Number	is, is not, higher than, lower than, is blank, is not blank
Image	is blank, is not blank
File	is blank, is not blank
Address	contains, does not contain, is, is not, starts with, ends with, is blank, is not blank, near
Name	contains, does not contain, is, is not, starts with, ends with, is blank, is not blank
Link	is, is not, is blank, is not blank
Email	contains, does not contain, is, is not, starts with, ends with, is blank, is not blank
Phone	contains, does not contain, is, is not, starts with, ends with, is blank, is not blank
Rich Text	contains, does not contain, is, is not, starts with, ends with, is blank, is not blank
Currency	contains, does not contain, is, is not, starts with, ends with, is blank, is not blank
Auto Increment	contains, does not contain, is, is not, starts with, ends with, is blank, is not blank
Timer	is, is not, higher than, lower than, is blank, is not blank
Rating	is, is not, higher than, lower than, is blank, is not blank
Text Formula	contains, does not contain, is, is not, starts with, ends with, is blank, is not blank
Signature	is blank, is not blank