I saw in this code example for a validation of an entry, that they use " %P " in the comparison, what exactly does it do and why should it be placed?
entry .amount -validate key -validatecommand {
expr {[string is int %P] || [string length %P]==0}
}
When you use -validatecommand you are specifying a validation for your entry, which is the one inside the brackets, and to bring the value to validate inside your condition you pull it with %P .
In the case of your validation, you are looking to check that the value of the entry is a string with 32-bit integer format or is an empty string.
the %P is used to return whether the clock time is tomorrow am or afternoon pm.
clock format [clock seconds] -format "%H:%m %P" returns whether it is am or pm