The total text advance distance includes the advance value on the glyphs (horizontal or vertical), kerning effects, letter-spacing effects, word-spacing effects, and adjustments because of the dx and dy attributes on tSpan elements.
If multiple consecutive characters are rendered inseparably (for example, as a single glyph or a sequence of glyphs, or because the range encompasses half of a surrogate pair), and if the nchars parameter is greater than 0, the measured range (i.e., total advance distance) is expanded so that each of the inseparable characters are included.
float retVal = object.getSubStringLength(charnum, nchars);
- Scalable Vector Graphics: Text, Section 10.17.1
Microsoft Developer Network: [Windows Internet Explorer API reference Article]