The Validate Like property instructs the form compiler to set the field properties that are defined in the .val database schema file for the specified column.
Specifying the Validate Like property is equivalent to writing in the field definition all the properties that are assigned to table.column in the .val databse schema file generated from the syscolval table.
Note that .val properties are taken automatically from the schema file if the field is linked to table.column in the field name specification. The Validate Like property is usually specified for FORMONLY fields.
The Validate Like property is evaluated at compile time, not at runtime. If the database schema file changes, you should recompile all your forms.
Even if all of the fields in the form are FORMONLY, the Validate Like property requires the form compiler to access the database schema file that contains the description of table.column.