Instead of character based string exclusion, excluding the entire search string

[mifrank-cg]

The string validation str(exclude='abcd') prohibits the occurrence of each single character of the exclude string.
But I would like to prohibit the occurrence of the entire string "abcd". So, I would like to prohibit specific words.
Unfortunately, the options are too many, so I cannot allow them with "enum", instead I would like to define the not allowed words in my yaml file.