diff --git a/circumstance.go b/circumstance.go
new file mode 100644
index 0000000..9a03e1d
--- /dev/null
+++ b/circumstance.go
@@ -0,0 +1,67 @@
+package eol
+
+import (
+	"sourcecode.social/reiver/go-opt"
+)
+
+// internalCircumstance is primarily used to help to create informative error messages.
+//
+// internalCircumstance contains the end-of-line sequence and the character-number within that end-of-line sequence.
+//
+// Example end-of-line sequences are:
+//
+//	• "\n"
+//	• "\r"
+//	• "\r\n"
+//	• "\u0085"
+//	• "\u2028"
+//
+// No end-of-line sequence can also be specified if it is unknown.
+// For example eol.ReadEOL() does NOT know the end-of-line sequence ahead of time.
+//
+// The character-number is 1-indexed.
+// Meaning that the 1st character is 1 (and not 0).
+//
+// Creating an internalCircumstance usually looks something like these:
+//
+//	var circumstance internalCircumstance = specifyCircumstance(opt.Nothing[string](), 1)
+//
+//	var circumstance internalCircumstance = specifyCircumstance(opt.Something]("\n"), 1)
+//
+//	var circumstance internalCircumstance = specifyCircumstance(opt.Something]("\r"), 1)
+//
+//	var circumstance internalCircumstance = specifyCircumstance(opt.Something]("\r\n"), 1)
+//
+//	var circumstance internalCircumstance = specifyCircumstance(opt.Something]("\r\n"), 2)
+//
+//	var circumstance internalCircumstance = specifyCircumstance(opt.Something]("\u0085"), 1)
+//
+//	var circumstance internalCircumstance = specifyCircumstance(opt.Something]("\u2028"), 1)
+//
+// These would then be passed to some type of error.
+// For example:
+//
+//	var err error = errNotFound(circumstance, expected, actual)
+//
+//	var err error = errProblemReadingRune(circumstance, err)
+//
+//	var err error = errProblemUnreadingRune(circumstance, err, r)
+type internalCircumstance struct {
+	eolSequence opt.Optional[string]
+	characterNumber uint64
+}
+
+func specifyCircumstance(eolSequence opt.Optional[string], characterNumber uint64) internalCircumstance {
+	return internalCircumstance{
+		eolSequence:eolSequence,
+		characterNumber:characterNumber,
+	}
+}
+
+func (receiver internalCircumstance) CharacterNumber() uint64 {
+	return receiver.characterNumber
+}
+
+func (receiver internalCircumstance) EOLSequence() opt.Optional[string] {
+	return receiver.eolSequence
+}