One of the important topics in the Russian language regarding punctuation is called “Separation of applications”. In order to deal with this complex issue, you first need to define what should be understood by the term "application" in relation to the Russian language.
First of all, it should be understood that the application is a definition. But it is expressed either by a noun characterizing the subject on the other hand, giving it a different name or indicating nationality, profession, rank or determining the degree of kinship (as opposed to the usual definition expressed by an adjective, participle or qualitative numeral), or an expression consisting of a few words. A single application noun should be used in the same case and number as the noun, which it defines and complements.
An example is the previous sentence with the isolation of “noun” or such a proposal with a separate application:
A little house (I.P., unit h.), A wretched shack (I.P., unit h.), Hunched over under a thatched roof, glanced gloomily at the world with his blind eyes.
By the way, you should pay attention to the fact that in a sentence with a single application, both words - both definable and application - are common nouns with a hyphen between them. This is one of the basic rules that explains the isolation of applications expressed by a single common noun.
If one of the nouns is expressed by a proper noun, then only in the case when a proper noun appears before a household word, a hyphen is required. For instance:
The Moscow River smoothly carried its waters past us, slyly winking at the sun glare.
There is no hyphen, since the proper name is used after the common noun.
The Moscow River smoothly carried its waters past us, slyly winking at the sun glare.
The Moscow River requires a hyphen between words, because the proper name " Moscow " is in front of the application, a common household name.
Separate definitions and applications that relate to the personal pronoun should always be highlighted with commas, regardless of their position — before or after the pronoun. For instance:
As a young Russian citizen, joining the ranks of the Young Firefighters detachment, I swear to comply with the detachment’s charter.
Tired, they quietly entered the warm, heated hut.
Separation of applications that are not related to pronouns obeys slightly different rules. Here, the location of the application plays a large role. For instance:
The mystery, bloody and terrible, went with her to the grave.
(Compare. Bloody and terrible secret and went with her to the grave.)
From the examples we see that isolation of applications takes place only if the application is located behind the defined word (Mystery, bloody and scary, ...). If it is in front of the main word, then you do not need to put any punctuation marks (an example is the sentence marked "Wed")
A common application, which includes a noun, is isolated in any case, regardless of its location, and if it defines or clarifies a common noun. For instance:
My sister, a beautiful woman with long braids to the waist, was a simple and sociable girl.
(Wed Beauty with long braids to the waist, my sister was a simple and sociable girl).
It should be noted that in some cases, when the author wants to attach more importance to the application at the end of the sentence, they isolate it with a dash and not a comma.
So the month of November is coming to an end - the last month before giving birth.
There is one more peculiarity of character placement during isolation, which should be taken into account when writing. This feature of applications with “how” unions concerns. If this union can be replaced with the phrase "as", then the signs should not be put in the application. For instance:
Classmates as potential suitors by girls were not considered in principle.
If you treat applications with due attention, then it is quite possible to avoid mistakes when placing punctuation marks with them.