Having trouble with the maximum text length in textboxes.

My text box has a maximum text length of 3,000. To test it, I filled out the box with a series of digits (1234567890) across the line and down the rows, but the total number of characters I entered is far less than the maximum text length I set for the box. So, is a “text length” anything between two spaces? How does this option work? What are its rules?