Fixes intelsdi-x#1477, Added information about not recommended charac…

…ters as a namespace separators in the task manifest

docs/TASKS.md

@@ -207,7 +207,13 @@ More information about the architecture behind this can be found [here](DISTRIBU
 
 #### collect
 
-The collect section describes which metrics are requested to be collected.
+The collect section describes which metrics, indicated by namespaces, are requested to be collected.
+
+Elements of namespace are separated by **namespace separator** which can be defined in the task manifest as different characters,
+with some limitations specific for format of the task manifest.
+It is not recommended to use following characters in the task manifest as the namespace separator:
+- for YAML: `|`,`#`, `$`, `>`,`*`, `,`,`[`, `]`,`{`,`}`,`!`,`"`, `` ` ``,`%`,`@`
+- for JSON: ` \ `, `$`,`"`, `*`
 
 Metrics can be enumerated using: