Selects documents by matching the character string you specify with a portion of the strings of the values stored in a specific document field. The characters that comprise the string can occur at the beginning of a field value, within a field value, or at the end of a field value. The syntax for SUBSTRING is the same as that for MATCHES. See the example for MATCHES under the topic "visual arts" in "Sample Topic Outlines." The example assumes that the field TITLE has been created for the collection.