Clarify trigger event context (#2965)

Resolves #2538

Co-authored-by: Dia Patience Daur <[email protected]>

Author: p7nov

doc/book/box/triggers.rst

@@ -3,15 +3,14 @@
 .. _triggers:
 .. _triggers-box_triggers:
 
-================================================================================
 Triggers
-================================================================================
+========
 
 **Triggers**, also known as **callbacks**, are functions which the server
 executes when certain events happen.
 
 To associate an event with a callback,
-one should pass the callback to the corresponding :samp:`on_{event}` function:
+pass the callback to the corresponding :samp:`on_{event}` function:
 
 * :doc:`/reference/reference_lua/box_session/on_connect` or
   :doc:`/reference/reference_lua/box_session/on_disconnect`,
@@ -47,12 +46,12 @@ All triggers have the following characteristics:
 * There can be multiple triggers for one event. In this case, triggers are
   executed in the reverse order that they were defined in.
 
-* Triggers must work within the event context. However, effects are undefined
-  if a function contains requests which normally could not occur immediately
-  after the event, but only before the return from the event. For example, putting
-  `os.exit() <http://www.lua.org/manual/5.1/manual.html#pdf-os.exit>`_ or
-  :doc:`/reference/reference_lua/box_txn_management/rollback` in a trigger
-  function would be bringing in requests outside the event context.
+* Triggers must work within the event context, that is, operate variables passed
+  as the trigger function arguments. Triggers should not affect the global state
+  of the program or change things unrelated to the event. If a trigger performs
+  such calls as, for example, `os.exit() <http://www.lua.org/manual/5.1/manual.html#pdf-os.exit>`_
+  or :doc:`/reference/reference_lua/box_txn_management/rollback`, the result of
+  its execution is undefined.
 
 * Triggers are replaceable. The request to "redefine a trigger" implies
   passing a new trigger function and an old trigger function

locale/ru/LC_MESSAGES/book/box/triggers.po

@@ -11,10 +11,10 @@ msgstr ""
 "событий."
 
 msgid ""
-"To associate an event with a callback, one should pass the callback to the "
+"To associate an event with a callback, pass the callback to the "
 "corresponding :samp:`on_{event}` function:"
 msgstr ""
-"Чтобы связать событие с колбэк-функцией, необходимо передать её в "
+"Чтобы связать событие с колбэк-функцией, передайте её в "
 "соответствующую функцию обработки событий :samp:`on_{event}`:"
 
 msgid ""
@@ -110,20 +110,20 @@ msgstr ""
 "определили."
 
 msgid ""
-"Triggers must work within the event context. However, effects are undefined "
-"if a function contains requests which normally could not occur immediately "
-"after the event, but only before the return from the event. For example, "
-"putting `os.exit() <http://www.lua.org/manual/5.1/manual.html#pdf-os.exit>`_"
-" or :doc:`/reference/reference_lua/box_txn_management/rollback` in a trigger"
-" function would be bringing in requests outside the event context."
-msgstr ""
-"Триггеры должны работать в контексте события. Однако результат не определен,"
-" если функция содержит запросы, которые при нормальных условиях не могут "
-"быть выполнены непосредственно после события, а только после возврата из "
-"события. Например, если указать `os.exit() "
-"<http://www.lua.org/manual/5.1/manual.html#pdf-os.exit>`_ или "
-":doc:`/reference/reference_lua/box_txn_management/rollback` в триггерной "
-"функции, запросы не будут выполняться в контексте события."
+"Triggers must work within the event context, that is, operate variables passed "
+"as the trigger function arguments. Triggers should not affect the global state "
+"of the program or change things unrelated to the event. If a trigger performs "
+"such calls as, for example, `os.exit() <http://www.lua.org/manual/5.1/manual.html#pdf-os.exit>`_ "
+"or :doc:`/reference/reference_lua/box_txn_management/rollback`, the result of "
+"its execution is undefined."
+msgstr ""
+"Триггеры должны работать в контексте события, то есть оперировать переменными, "
+"которые переданы как аргументы его функции. Триггеры не должны влиять на "
+"глобальное состояние программы или менять параметры, не связанные с событием. "
+"Если триггер выполняет такие вызовы, как, например, "
+"`os.exit() <http://www.lua.org/manual/5.1/manual.html#pdf-os.exit>`_ "
+"или :doc:`/reference/reference_lua/box_txn_management/rollback`, "
+"результат его выполнения не определен."
 
 msgid ""
 "Triggers are replaceable. The request to \"redefine a trigger\" implies "