I defined a comma separated sequence, and the global encoding in that schema
is "US-ASCII". This sequence consists of two elements, the first being a
binary string in utf-8, and the second being a binary string in utf-16be.
My test defines a document with the documentPart type set to "byte". I
specify the first element in utf-8, the delimiter in us-ascii, and the
second element in utf-16be. Currently I get this error:

[info] - test_multi_encoding_02 *** FAILED ***
[info] edu.illinois.ncsa.daffodil.exceptions.Abort: Invariant broken. Runtime parsers should not throw exceptions: scala.MatchError: Some(DFDLCharReader at bitPos 0) (of class scala.Some)
[info] edu.illinois.ncsa.daffodil.exceptions.Assert$.abort(Assert.scala:85)
[info] edu.illinois.ncsa.daffodil.exceptions.Assert$.invariantFailed(Assert.scala:122)
[info] edu.illinois.ncsa.daffodil.processors.AltCompParser$$anonfun$parse$4.apply(Parser.scala:353)
[info] edu.illinois.ncsa.daffodil.processors.AltCompParser$$anonfun$parse$4.apply(Parser.scala:346)
[info] at edu.illinois.ncsa.daffodil.exceptions.Assert$.abort(Assert.scala:85)
[info] at edu.illinois.ncsa.daffodil.exceptions.Assert$.invariantFailed(Assert.scala:122)
[info] at edu.illinois.ncsa.daffodil.processors.AltCompParser$$anonfun$parse$4.apply(Parser.scala:353)
[info] at edu.illinois.ncsa.daffodil.processors.AltCompParser$$anonfun$parse$4.apply(Parser.scala:346)
[info] at scala.collection.LinearSeqOptimized$class.foreach(LinearSeqOptimized.scala:59)
[info] at scala.collection.immutable.List.foreach(List.scala:76)
[info] at edu.illinois.ncsa.daffodil.processors.AltCompParser.parse(Parser.scala:346)
[info] at edu.illinois.ncsa.daffodil.processors.Parser.parse1(Parser.scala:132)
[info] at edu.illinois.ncsa.daffodil.processors.SeqCompParser$$anonfun$parse$3.apply(Parser.scala:319)
[info] at edu.illinois.ncsa.daffodil.processors.SeqCompParser$$anonfun$parse$3.apply(Parser.scala:317)

I created another test
(multi_encoding_4) that uses a sequence with lengthKind="delimited" and no
delimiters, with each element using a different encoding, as you mentioned
previously. This is the error I receive

[info] - test_multi_encoding_04 *** FAILED ***
[info] scala.MatchError: Some(DFDLCharReader at bitPos 0) (of class scala.Some)
[info] at edu.illinois.ncsa.daffodil.processors.TextReader$class.getReader(Primitives.scala:2933)
[info] at edu.illinois.ncsa.daffodil.processors.StringDelimitedEndOfData.getReader(Primitives.scala:576)
[info] at edu.illinois.ncsa.daffodil.processors.StringDelimitedEndOfData$$anon$7$$anonfun$parse$8.apply(Primitives.scala:624)
[info] at edu.illinois.ncsa.daffodil.processors.StringDelimitedEndOfData$$anon$7$$anonfun$parse$8.apply(Primitives.scala:591)
[info] at edu.illinois.ncsa.daffodil.processors.WithParseErrorThrowing$class.withParseErrorThrowing(Parser.scala:220)
[info] at edu.illinois.ncsa.daffodil.processors.StringDelimitedEndOfData.withParseErrorThrowing(Primitives.scala:576)
[info] at edu.illinois.ncsa.daffodil.processors.StringDelimitedEndOfData$$anon$7.parse(Primitives.scala:589)
[info] at edu.illinois.ncsa.daffodil.processors.Parser.parse1(Parser.scala:132)
[info] at edu.illinois.ncsa.daffodil.processors.SeqCompParser$$anonfun$parse$3.apply(Parser.scala:319)
[info] at edu.illinois.ncsa.daffodil.processors.SeqCompParser$$anonfun$parse$3.apply(Parser.scala:317)