v0.2.2 fixes: split only text sources, report a mode change once, don't block on open

doc/env.md

@@ -8,8 +8,10 @@ Options are copied. Custom transforms run outside Config locks and may inspect C
 Environment values are stored as strings and validated against registered types
 before any part of the replacement is published. Numbers use decimal text; durations
 use Go duration syntax; timestamps use RFC3339Nano-compatible text. Slices and arrays
-use comma-separated elements without an escaping convention. Empty text gives an
-empty slice. Values larger than MaxValueSize are rejected.
+use comma-separated elements without an escaping convention. An empty variable is
+unset, so a template may leave one blank. Two paths whose names map to one set
+variable (`a.b_c` and `a_b.c` both to `APP_A_B_C`) fail the load. Values larger than
+MaxValueSize are rejected.
 
 `RegisterWithEnv` and a struct field's `env` tag load an explicitly named variable
 during registration. Later `LoadEnv` calls use the configured transform/whitelist,