General the ASCII import filter accept files with UNIX, Mac and Windows line end characters. Each line should contain at least one number. Numbers in the line will be separated by any character which could not be part of a number.
If the Plot builtin import filter is not able to import your data file you can build your own Perl based import filter in the Macro Inspector.
The import dialog allows to select between two modes of importing ASCII data.
X Column: Defines which column should be the X column starting with 1 for the first column.
Treat all columns as Y values: If checked all columns will be interpreted a Y values and the X values will be generated as sequence number. This allows also to import files which have only one column.
Field Separator: Defines the field separator for ASCII import. Explicit definition of the separator allows to import files with empty fields.
Ignore Lines Containing: Lines in your data file which contains this string will be ignored.
Comment Character Sequence: Anything in a line behind this string will be ignored.
Ignore lines which not begin with a number: If checked only lines beginning with a number will be processed.