I am not sure if you are referring to "technical features" in regards to technical aspects of the piece (such as the setting directions) or in regards to literary devices/features (such as similes or alliteration). Therefore, the answer will address both aspects in Dylan Thomas' "Under Milk Wood."
In the opening of the drama, many different directions are given to anyone wishing to produce the play. The staging direction include very technical language. Here are some examples:
Please locate and pre -set the following effects:
1) Effect 1 – Dreamy style echo
2) Effect 2 – Interior Wood Room (a town hall)
3) Effect 3 – Interior Stone Room (like a vault or crypt)
4) Effect 4 – On the phone – or tinny alteration of voice
Outside of these technical features offered in the setup of the drama, many other different examples of technical aspects exist.
The opening dialogue is filled with different examples of figurative language.
To begin at the beginning...
It is spring, moonless night in the small town, starless and bible black. The cobblestreets silent and the hunched, courters’ and rabbits’ wood, limping invisibly down to the sloe black, slow, black, crow black, fishing boat-bobbing sea.
The houses are blind as moles, though moles see fine tonight in the snouting, velvet dingles, or blind as Captain Cat there in the muffled middle by the pump and the town clock, the shops in mourning, the Welfare Hall in widow’s weeds. And all the people of the lulled and dumbfound town are sleeping now.
Alliteration is exemplified in the opening: "To begin at the beginning." The consonant sound "b" is repeated in "begin" and "beginning."
Simile is exemplified in the following: "The houses are as blind as moles." Here, houses are compared to moles using the word "as."
Imagery is exemplified through the numerous descriptions provided regarding the sleepy town. These descriptions allow the reader of the play to create a mental image of the town.