formalise interaction between overlapping raw text marks

[urieli]

If one text marker replaces "abc" with "Sheep" and another replaces "b" with "Horse", the result for "JJJabcKKK" will be "JJJSheepHorseKKK". Ideally, we want "JJJSheepKKK".

Thus, we need to define rules for overlapping matches. Some are permissible, others need to be ignored.