1. A method for determining a line height for a string of text, the text being organized in clusters, each cluster being a rendering unit of the string of text identified by an amount of printed matter between points where a cursor can be inserted therein, the string of text being rendered in a font size, the font size being in terms of an em, each em identified by a square of the type, the method comprising: determining a value representing a number of clusters per em in the string of text; and scaling a default line height by an exponential function.