A most excellent proof, too small to fi—!

Question

You sit at home, rubbing your hands in a most evil fashion. This time, I'll be able to set the community A-SPIN! I'll merely claim that I have proven this problem (which is of no doubt improvable) inside this book here… You open to the first relevant page. You scrawl those words…

You are, of course, the evil Fermat! Haha, just kidding. You know it didn't happen like this; this is merely the narrative of his evil twin, Format. Format here is too lazy to condense his “proof” into the margin. He has therefore called upon you to do it for him.

Objective Given a proof (string), and a page (text block), "write" into the margin the proof.

Valid page rules

A text block contains a page if and only if it meets the following requirements:

• The top and bottom borders are of the form -{10,}\+$ (Regular expression for - at least ten times until a +, then the end of the line).
• Every non-top and non-bottom line must end with a |. There will be at least one such line.
• There will be at least five spaces from the last | in each line.
• All lines are the same width.

So the following is a valid page (the .s are for showing where the maximal margin border is):

-----------------+
Lorem Ipsum.     |
and other  .     |
latin crud .     |
           .     |
        EOF.     |
-----------------+

Here is another page with a wider margin:

------------------------+
Hello world!   .        |
How are you, to.        |
day? --Mme. B  .        |
               .        |
------------------------+

You are to write the given string in the margin, maintaining words that you can, as far as you can. For example, if hello fits on the next line, do not break it on the current line.

I/Os

Filler text

Proof: This is a most excellent proof, too small for anyone!
Text:                       ; not a leading newline
------------------------+
Hello world!            |
How are you, to         |
day? --Mme. B           |
                        |
------------------------+
Output: 
------------------------+
Hello world!    This a  |
How are you, to most    |
day? --Mme. B   excellen|
                t proof,|
------------------------+    

Proof: Execute the member as an example to the others!
Text:
------------------------------------------------+
Contrary to popular belief, Lorem               |
Ipsum is not simply random text.                |
It has roots in a piece of classical            |
Latin literature from 45 BC, making             |
it over 2000 years old. Richard                 |
McClintock, a Latin professor at                |
Hampden-Sydney College in Virginia,             |
looked up one of the more obscure               |
Latin words, consectetur, from a                |
Lorem Ipsum passage, and going through          |
the cites of the word in classical              |
literature, discovered the undoubtable          |
source. Lorem Ipsum comes from...               |
------------------------------------------------+
Output:
------------------------------------------------+
Contrary to popular belief, Lorem      Execute  |
Ipsum is not simply random text.       the      |
It has roots in a piece of classical   member as|
Latin literature from 45 BC, making    an       |
it over 2000 years old. Richard        example  |
McClintock, a Latin professor at       to the   |
Hampden-Sydney College in Virginia,    others!  |
looked up one of the more obscure               |
Latin words, consectetur, from a                |
Lorem Ipsum passage, and going through          |
the cites of the word in classical              |
literature, discovered the undoubtable          |
source. Lorem Ipsum comes from...               |
------------------------------------------------+

Proof: Consider supercalifragilisticexpialidocious. Therefore, x.
Output:
-----------------------------------------+
sections 1.10.32 and                     |
1.10.33 of "de Finibus                   |
Bonorum et Malorum"                      |
(The Extremes of Good                    |
and Evil) by Cicero,                     |
written in 45 BC. This                   |
book is a treatise on                    |
the theory of ethics,                    |
very popular during the                  |
Renaissance. The first                   |
line of Lorem Ipsum,                     |
"Lorem ipsum dolor sit                   |
amet..", comes from a                    |
line in section 1.10.32.                 |
-----------------------------------------+
Output: Consider supercalifragilisticexpialidocious. Therefore, x.
-----------------------------------------+
sections 1.10.32 and     Consider        |
1.10.33 of "de Finibus   supercalifragili|
Bonorum et Malorum"      sticexpialidocio|
(The Extremes of Good    us. Therefore, x|
and Evil) by Cicero,     .               |
written in 45 BC. This                   |
book is a treatise on                    |
the theory of ethics,                    |
very popular during the                  |
Renaissance. The first                   |
line of Lorem Ipsum,                     |
"Lorem ipsum dolor sit                   |
amet..", comes from a                    |
line in section 1.10.32.                 |
-----------------------------------------+

Proof: Alex is a bird. All birds can fly. All things that fly are wrong. Ergo, Alex is wrong.
Text:
----------+
Sorry     |    ; 5 spaces. 
----------+
Output:
----------+
Sorry Alex|
----------+

---

This is a code-golf, so the shortest program in bytes wins!

---

Leaderboard

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body{text-align:left!important}#answer-list,#language-list{padding:10px;width:290px;float:left}table thead{font-weight:700}table td{padding:5px}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <link rel="stylesheet" type="text/css" href="//cdn.sstatic.net/codegolf/all.css?v=83c949450c8b"> <div id="answer-list"> <h2>Leaderboard</h2> <table class="answer-list"> <thead> <tr><td></td><td>Author</td><td>Language</td><td>Size</td></tr></thead> <tbody id="answers"> </tbody> </table> </div><div id="language-list"> <h2>Winners by Language</h2> <table class="language-list"> <thead> <tr><td>Language</td><td>User</td><td>Score</td></tr></thead> <tbody id="languages"> </tbody> </table> </div><table style="display: none"> <tbody id="answer-template"> <tr><td>{{PLACE}}</td><td>{{NAME}}</td><td>{{LANGUAGE}}</td><td>{{SIZE}}</td><td><a href="{{LINK}}">Link</a></td></tr></tbody> </table> <table style="display: none"> <tbody id="language-template"> <tr><td>{{LANGUAGE}}</td><td>{{NAME}}</td><td>{{SIZE}}</td><td><a href="{{LINK}}">Link</a></td></tr></tbody> </table>

Answer 1

Python 2, 334

p=open("f.txt",'r').readlines()
r,S,p=p[0][7:],p[2].strip(),p[3:-1]
import textwrap as t,itertools as i
m,l=max([len(s[:-5].strip()) for s in p]),len(S)-2
P = i.izip_longest(["{} {{:{}}}|".format(s[:m],l-m) for s in p],t.wrap(r,l-m),fillvalue="")
print S
for q in P:
 if not q[0]:break
 print q[0].format(q[1])
print S

Sample IO with contents of f.txt followed by code output

Case 1

Proof: This is a most excellent proof, too small for anyone!
Text:                       
------------------------+
Hello world!            |
How are you, to         |
day? --Mme. B           |
                        |
------------------------+

------------------------+
Hello world!    Proof:  |
How are you, to This is |
day? --Mme. B   a most e|
                xcellent|
------------------------+

Case 2

Proof: Consider supercalifragilisticexpialidocious. Therefore, x.
Output:
-----------------------------------------+
sections 1.10.32 and                     |
1.10.33 of "de Finibus                   |
Bonorum et Malorum"                      |
(The Extremes of Good                    |
and Evil) by Cicero,                     |
written in 45 BC. This                   |
book is a treatise on                    |
the theory of ethics,                    |
very popular during the                  |
Renaissance. The first                   |
line of Lorem Ipsum,                     |
"Lorem ipsum dolor sit                   |
amet..", comes from a                    |
line in section 1.10.32.                 |
-----------------------------------------+

-----------------------------------------+
sections 1.10.32 and     Consider superca|
1.10.33 of "de Finibus   lifragilisticexp|
Bonorum et Malorum"      ialidocious.    |
(The Extremes of Good    Therefore, x.   |
and Evil) by Cicero,                     |
written in 45 BC. This                   |
book is a treatise on                    |
the theory of ethics,                    |
very popular during the                  |
Renaissance. The first                   |
line of Lorem Ipsum,                     |
"Lorem ipsum dolor sit                   |
amet..", comes from a                    |
line in section 1.10.32.                 |
-----------------------------------------+

Case 3

Proof: Alex is a bird. All birds can fly. All things that fly are wrong. Ergo, Alex is wrong.
Text:
----------+
Sorry     |   
----------+

----------+
Sorry Alex|
----------+