Instructions are also embedded in fonts to tell the operating system how to properly output different character sequences. A simple solution to the placement of combining marks or diacritics is <answer>assigning the marks a width of zero and placing the glyph itself to the left or right of the left sidebearing</answer> (depending on the direction of the script they are intended to be used with). A mark handled this way will appear over whatever character precedes it, but will not adjust its position relative to the width or height of the base glyph; it may be visually awkward and it may overlap some glyphs. Real stacking is impossible, but can be approximated in limited cases (for example, Thai top-combining vowels and tone marks can just be at different heights to start with). Generally this approach is only effective in monospaced fonts, but may be used as a fallback rendering method when more complex methods fail.
what is a solution to the placement of combining marks? 
assigning the marks a width of zero and placing the glyph itself to the left or right of the left sidebearing