In all of the examples I’ve seen of the “contain” meaning, the object being contained is the subject. That seems to match with the most common definition of 入る, “to enter”. But all of the dictionaries I’ve seen list the definition as “to contain/include”.
Ex: Wikitionary:
[旅りょ費ひ](https://en.wiktionary.org/wiki/%E6%97%85%E8%B2%BB#Japanese)には[朝あさ晩ばん](https://en.wiktionary.org/wiki/%E6%9C%9D%E6%99%A9#Japanese)の[食しょく事じ代だい](https://en.wiktionary.org/w/index.php?title=%E9%A3%9F%E4%BA%8B%E4%BB%A3&action=edit&redlink=1)も**入はいっています**。
The travel expenses also **include** the meal plan for both morning and evening.
Ex: Maggie Sensei
この料理には何が入っていますか？
What is in this food?
料金にはサービス料が入っていません。
The service charge is not included in the fee.
​
Or is this sort of subject ambiguity not considered significant?
2 comments
> Does 入る mean “to be contained/included” instead of “to contain/include”?
Yes; 入る is always intransitive.
> 旅費には 朝晩の食事代も **入っています**。
> The travel expenses also **include** the meal plan for both morning and evening.
Well, this is just a matter of liberties being taken in translation (as they often pretty much need to be, though perhaps not so much here).
In the original sentence, 食事代 (the meal plan) is the *subject* of 入る, and 旅費 is marked with に as the “space” where the 食事代 has 入るed (and is still 入っている).
– Aが Bに 入る = ”A enters B”
– Aが Bに 入っている = ”A is in B” (A has entered B and is still in B — “enduring resultant state” nuance of ～ている)
– 食事代が 旅費に 入っている = ”the meal plan is (included) in the travel expenses” = ”the travel expenses include the meal plan”
– 旅費には 朝晩の食事代も 入っています = ”the meal plan for both morning and evening is included in the travel expenses too” = ”the travel expenses also include the meal plan for both morning and evening”
In the example about trip expenses, 入る would mean to “be in (something)” (i.e. morning and evening meals are included in the expenses). The translation alters things a bit to make it sound more natural. Notice the basic structure is (Xには)Yが入っている, i.e. Y enters/is part of X.
If you’re wondering about including, 含める(ふくめる) means to include (e.g. in a group). 私を含めて3人です means “3 people, myself included”.
You also have 含む, which means to contain, comprise (as in “a set comprising 10 numbers”).