A dialog function needs an identifier for each dialog box control that it acts on. The dialog function uses string identifiers. String identifiers are the same as the identifiers used in the dialog record.
CheckBox 8, 56, 203, 16, "Check to display controls",. Chk1
The control’s identifier and label are different. An identifier begins with a period and is the last parameter in a dialog box control instruction. In the sample code above "Check to display controls" is the label and .chk1 is the identifier.