readme: update _ instead of : changes for coder/filter attributes

README.md

@@ -126,11 +126,11 @@ Whenever the data needs to be either (pre)processed by multiple (2+) filters or
 
 The rules for this **Multiple Compressor(s)/Preprocessor(s)** list are as follows:  
 - all (additional) methods/coders need to be specified in the output hash format (the fields `coder attributes` and `preprocessor attributes` accordingly), even if they have no attributes
-- the format is a comma-separated list of type and order indicator (for both fields: compressor and preprocessor attributes), followed by a colon (:), followed by the attribute itself
+- the format is a comma-separated list of type and order indicator (for both fields: compressor and preprocessor attributes), followed by an underscore (_), followed by the attribute itself
 - the **first attribute**/item/codec for both fields (compressor and preprocessor attributes) needs no type and order indicator, only attributes
 - the type and position/order of the first decompressor/filter are implied (it's always the first decompressor/filter and the type is in the `data type indicator` field)
 - this also means that the field `data type indicator` (see format above) only indicates the **first** decompressor (if used) and (also, if used) the first preprocessing filter (this is also due to compatibility reasons with older formats)
-- for the additional (2+) decompressors/filters, the first number after the comma is the type and order indicator, after which follows a colon (:) and the attributes themself (could be empty/no attribute value for some codecs)
+- for the additional (2+) decompressors/filters, the first number after the comma is the type and order indicator, after which follows an underscore (_) and the attributes themself (could be empty/no attribute value for some codecs)
 - special case: the `coder attributes` field could start with a comma (and has also a type and order indicator) in the unlikely case where during archive generation a filter was applied after the final compression of the data. Otherwise it's always the case that the decompressor needs to be applied first
 
 Multiple Compressor(s)/Preprocessor(s) type and order indicator (it is one combined field/number):