interpreter: Introduce StringHolder

Another commit in my quest to rid InterpreterBase from all higher
level object processing logic.

Additionally, there is a a logic change here, since `str.join` now
uses varargs and can now accept more than one argument (and supports
list flattening).

2 files changed, 6 insertions, 0 deletions

diff --git a/docs/markdown/Reference-manual.md b/docs/markdown/Reference-manual.md
index 8ef36de..31ed77e 100644
--- a/docs/markdown/Reference-manual.md
+++ b/docs/markdown/Reference-manual.md
@@ -2268,6 +2268,7 @@ are immutable, all operations return their results as a new string.
 
 - `join(list_of_strings)`: the opposite of split, for example
   `'.'.join(['a', 'b', 'c']` yields `'a.b.c'`.
+  *(Since 0.60.0)* more than one argument is supported and lists will be flattened.
 
 - `replace('old_substr', 'new_str')` *(since 0.58.0)*: replaces instances of
   `old_substr` in the string with `new_str` and returns a new string
diff --git a/docs/markdown/snippets/str_join.md b/docs/markdown/snippets/str_join.md
new file mode 100644
index 0000000..b430d66
--- /dev/null
+++ b/docs/markdown/snippets/str_join.md
@@ -0,0 +1,5 @@
+## Relax restrictions of `str.join()`
+
+Since 0.60.0, the [[str.join]] method can take an arbitrary number of arguments
+instead of just one list. Additionally, all lists past to [[str.join]] will now
+be flattened.