Clarify mutable objects usage

Only Environment and ConfigurationData are mutable. However, only
ConfigurationData becomes immutable after first use which is
inconsistent.

This deprecates modification after first use of Environment object and
clarify documentation.

1 files changed, 1 insertions, 1 deletions

diff --git a/docs/markdown/Configuration.md b/docs/markdown/Configuration.md
index 48f071e6c..b5875e55e 100644
--- a/docs/markdown/Configuration.md
+++ b/docs/markdown/Configuration.md
@@ -39,7 +39,7 @@ use a single `configuration_data` object as many times as you like,
 but it becomes immutable after being passed to the `configure_file`
 function. That is, after it has been used once to generate output the
 `set` function becomes unusable and trying to call it causes an error.
-Copy of immutable `configuration_data` is still immutable.
+*Since 1.5.0* Copy of immutable `configuration_data` is however mutable.
 
 For more complex configuration file generation Meson provides a second
 form. To use it, put a line like this in your configuration file.