By default the File name expression is set to 'Wildcards' (also known as 'DOS Expression'). For this expression type you can search for multiple names by separating them by a semi-colon, e.g. to find all .txt or .xls files:
File name: *.txt;*.xls
If you want to search for two or more terms that must be in the file name use the ':' to separate the terms, e.g. to find all .txt files that have the word 'read' and 'history' in the name:
File name: *.txt:read:history
Boolean expressions
You can switch the expression type in the Options tab to 'Boolean' and the equivalent expressions would be:
File name: *.txt OR *.xls
Filename: *.txt AND read AND history
